diff --git a/src/Configuration/SystemConfiguration.php b/src/Configuration/SystemConfiguration.php
index cd5eda90..cfa36239 100644
--- a/src/Configuration/SystemConfiguration.php
+++ b/src/Configuration/SystemConfiguration.php
@@ -211,6 +211,16 @@ class SystemConfiguration implements SystemBundleConfiguration
     }
 
     // ========== Timesheet configurations ==========
+    /*
+        public function getTimesheetBreakWarningDuration(): int
+        {
+            return (int) $this->find('timesheet.rules.break_warning_duration');
+        }
+    */
+    public function getTimesheetLongRunningDuration(): int
+    {
+        return (int) $this->find('timesheet.rules.long_running_duration');
+    }
 
     public function getTimesheetDefaultBeginTime(): string
     {
@@ -352,6 +362,11 @@ class SystemConfiguration implements SystemBundleConfiguration
         return (bool) $this->find('theme.colors_limited');
     }
 
+    public function getThemeAutocompleteCharacters(): int
+    {
+        return (int) $this->find('theme.autocomplete_chars');
+    }
+
     public function getThemeColorChoices(): ?array
     {
         $config = $this->find('theme.color_choices');
diff --git a/src/Controller/SystemConfigurationController.php b/src/Controller/SystemConfigurationController.php
index 23cd2c27..df12da95 100644
--- a/src/Controller/SystemConfigurationController.php
+++ b/src/Controller/SystemConfigurationController.php
@@ -365,6 +365,22 @@ final class SystemConfigurationController extends AbstractController
                         ->setConstraints([
                             new GreaterThanOrEqual(['value' => 0])
                         ]),
+                    /*
+                    (new Configuration())
+                        ->setName('timesheet.rules.break_warning_duration')
+                        ->setType(IntegerType::class)
+                        ->setTranslationDomain('system-configuration')
+                        ->setConstraints([
+                            new GreaterThanOrEqual(['value' => 0])
+                        ]),
+                    */
+                    (new Configuration())
+                        ->setName('timesheet.rules.long_running_duration')
+                        ->setType(IntegerType::class)
+                        ->setTranslationDomain('system-configuration')
+                        ->setConstraints([
+                            new GreaterThanOrEqual(['value' => 0])
+                        ]),
                 ]),
             (new SystemConfigurationModel())
                 ->setSection(SystemConfigurationModel::SECTION_LOCKDOWN)
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index 6f5088f3..9cb98574 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -242,6 +242,15 @@ class Configuration implements ConfigurationInterface
                         ->scalarNode('lockdown_grace_period')
                             ->defaultNull()
                         ->end()
+                        ->scalarNode('lockdown_grace_period')
+                            ->defaultNull()
+                        ->end()
+                        ->integerNode('break_warning_duration')
+                            ->defaultValue(0)
+                        ->end()
+                        ->integerNode('long_running_duration')
+                            ->defaultValue(0)
+                        ->end()
                     ->end()
                 ->end()
             ->end()
diff --git a/src/Validator/Constraints/TimesheetLongRunning.php b/src/Validator/Constraints/TimesheetLongRunning.php
new file mode 100644
index 00000000..9694875c
--- /dev/null
+++ b/src/Validator/Constraints/TimesheetLongRunning.php
@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Validator\Constraints;
+
+final class TimesheetLongRunning extends TimesheetConstraint
+{
+    public const LONG_RUNNING = 'kimai-timesheet-long-running-01';
+
+    protected static $errorNames = [
+        self::LONG_RUNNING => 'TIMESHEET_LONG_RUNNING',
+    ];
+
+    public $message = 'Maximum duration of {{ value }} hours exceeded.';
+
+    public function getTargets()
+    {
+        return self::CLASS_CONSTRAINT;
+    }
+}
diff --git a/src/Validator/Constraints/TimesheetLongRunningValidator.php b/src/Validator/Constraints/TimesheetLongRunningValidator.php
new file mode 100644
index 00000000..2c586d0e
--- /dev/null
+++ b/src/Validator/Constraints/TimesheetLongRunningValidator.php
@@ -0,0 +1,69 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Validator\Constraints;
+
+use App\Configuration\SystemConfiguration;
+use App\Entity\Timesheet as TimesheetEntity;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+
+final class TimesheetLongRunningValidator extends ConstraintValidator
+{
+    private $systemConfiguration;
+
+    public function __construct(SystemConfiguration $systemConfiguration)
+    {
+        $this->systemConfiguration = $systemConfiguration;
+    }
+
+    /**
+     * @param TimesheetEntity $timesheet
+     * @param Constraint $constraint
+     */
+    public function validate($timesheet, Constraint $constraint)
+    {
+        if (!($constraint instanceof TimesheetLongRunning)) {
+            throw new UnexpectedTypeException($constraint, TimesheetLongRunning::class);
+        }
+
+        if (!\is_object($timesheet) || !($timesheet instanceof TimesheetEntity)) {
+            throw new UnexpectedTypeException($timesheet, TimesheetEntity::class);
+        }
+
+        if ($timesheet->isRunning()) {
+            return;
+        }
+
+        $maxMinutes = $this->systemConfiguration->getTimesheetLongRunningDuration();
+
+        if ($maxMinutes <= 0) {
+            return;
+        }
+
+        $duration = $timesheet->getEnd()->getTimestamp() - $timesheet->getBegin()->getTimestamp();
+        $minutes = (int) $duration / 60;
+
+        if ($minutes < $maxMinutes) {
+            return;
+        }
+
+        $format = new \App\Utils\Duration();
+        $hours = $format->format($maxMinutes * 60);
+
+        // raise a violation for all entries before the start of lockdown period
+        $this->context->buildViolation($constraint->message)
+            ->setParameter('{{ value }}', $hours)
+            ->setTranslationDomain('validators')
+            ->atPath('duration')
+            ->setCode(TimesheetLongRunning::LONG_RUNNING)
+            ->addViolation();
+    }
+}
diff --git a/templates/base.html.twig b/templates/base.html.twig
index c249a685..7d425f3c 100644
--- a/templates/base.html.twig
+++ b/templates/base.html.twig
@@ -275,7 +275,7 @@
                     locale: '{{ app.request.locale }}',
                     first_dow_iso: {{ iso_day_by_name(app.user.firstDayOfWeek) }},
                     twentyFourHours: {{ 'true'|hour24('false') }},
-                    autoComplete: {{ theme_config('autocomplete_chars') }},
+                    autoComplete: {{ kimai_config.themeAutocompleteCharacters }},
                     defaultColor: '{{ constant('App\\Constants::DEFAULT_COLOR') }}',
                     updateBrowserTitle: {% if app.user.preferenceValue('theme.update_browser_title') %}true{% else %}false{% endif %}
                 },
diff --git a/templates/user/stats.html.twig b/templates/user/stats.html.twig
index b0d49f8f..2470139b 100644
--- a/templates/user/stats.html.twig
+++ b/templates/user/stats.html.twig
@@ -177,6 +177,10 @@
             <span data-toggle="tooltip" title="{{ 'label.id'|trans }}: {{ user.id }}">{{ 'profile.about_me'|trans }}</span>
         {% endblock %}
         {% block box_body %}
+            <p>
+                <strong>{{ 'label.username'|trans }}</strong><br>
+                {{ user.username }}
+            </p>
             <p>
                 <strong>{{ 'profile.first_entry'|trans }}</strong><br>
                 {# FIXME use a configuration for it #}
diff --git a/tests/API/APIControllerBaseTest.php b/tests/API/APIControllerBaseTest.php
index cb7fc1f1..66459e2e 100644
--- a/tests/API/APIControllerBaseTest.php
+++ b/tests/API/APIControllerBaseTest.php
@@ -217,7 +217,7 @@ abstract class APIControllerBaseTest extends ControllerBaseTest
 
     /**
      * @param Response $response
-     * @param string[] $failedFields
+     * @param array<int, string>|array<string, mixed> $failedFields
      * @param bool $extraFields test for the error "This form should not contain extra fields"
      */
     protected function assertApiCallValidationError(Response $response, array $failedFields, bool $extraFields = false)
@@ -235,9 +235,21 @@ abstract class APIControllerBaseTest extends ControllerBaseTest
         self::assertArrayHasKey('children', $result['errors']);
         $data = $result['errors']['children'];
 
-        foreach ($failedFields as $fieldName) {
-            self::assertArrayHasKey($fieldName, $data, sprintf('Could not find validation error for field: %s', $fieldName));
+        foreach ($failedFields as $key => $value) {
+            $messages = [];
+            $fieldName = $value;
+            if (\is_string($key)) {
+                $fieldName = $key;
+                $messages = $value;
+                if (!\is_array($messages)) {
+                    $messages = [$value];
+                }
+            }
+            self::assertArrayHasKey($fieldName, $data, sprintf('Could not find validation error for field "%s" in list: %s', $fieldName, implode(', ', $failedFields)));
             self::assertArrayHasKey('errors', $data[$fieldName], sprintf('Field %s has no validation problem', $fieldName));
+            foreach ($messages as $i => $message) {
+                self::assertEquals($message, $data[$fieldName]['errors'][$i]);
+            }
         }
 
         $foundErrors = [];
diff --git a/tests/API/TimesheetControllerTest.php b/tests/API/TimesheetControllerTest.php
index d254c10e..d00646b1 100644
--- a/tests/API/TimesheetControllerTest.php
+++ b/tests/API/TimesheetControllerTest.php
@@ -389,7 +389,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $data = [
             'activity' => 1,
             'project' => 1,
-            'begin' => ($dateTime->createDateTime('- 16 hours'))->format('Y-m-d H:m:0'),
+            'begin' => ($dateTime->createDateTime('-8 hours'))->format('Y-m-d H:m:0'),
             'end' => ($dateTime->createDateTime())->format('Y-m-d H:m:0'),
             'description' => 'foo',
             'fixedRate' => 2016,
@@ -402,7 +402,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $this->assertIsArray($result);
         self::assertApiResponseTypeStructure('TimesheetEntity', $result);
         $this->assertNotEmpty($result['id']);
-        $this->assertTrue($result['duration'] == 57600 || $result['duration'] == 57660); // 1 minute rounding might be applied
+        $this->assertTrue($result['duration'] == 28800 || $result['duration'] == 28860); // 1 minute rounding might be applied
         $this->assertEquals(2016, $result['rate']);
     }
 
@@ -413,7 +413,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $data = [
             'activity' => 1,
             'project' => 1,
-            'begin' => ($dateTime->createDateTime('- 16 hours'))->format('Y-m-d H:m:0'),
+            'begin' => ($dateTime->createDateTime('-8 hours'))->format('Y-m-d H:m:0'),
             'end' => ($dateTime->createDateTime())->format('Y-m-d H:m:0'),
             'description' => 'foo',
             'fixedRate' => 2016,
@@ -426,7 +426,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $this->assertIsArray($result);
         self::assertApiResponseTypeStructure('TimesheetEntityFull', $result);
         $this->assertNotEmpty($result['id']);
-        $this->assertTrue($result['duration'] == 57600 || $result['duration'] == 57660); // 1 minute rounding might be applied
+        $this->assertTrue($result['duration'] == 28800 || $result['duration'] == 28860); // 1 minute rounding might be applied
         $this->assertEquals(2016, $result['rate']);
     }
 
@@ -443,7 +443,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
             'activity' => 1,
             'project' => 1,
             'user' => $user->getId(),
-            'begin' => ($dateTime->createDateTime('- 16 hours'))->format('Y-m-d H:m:0'),
+            'begin' => ($dateTime->createDateTime('- 8 hours'))->format('Y-m-d H:m:0'),
             'end' => ($dateTime->createDateTime())->format('Y-m-d H:m:0'),
             'description' => 'foo',
             'fixedRate' => 2016,
@@ -744,7 +744,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $client = $this->getClientForAuthenticatedUser(User::ROLE_USER);
         $this->importFixtureForUser(User::ROLE_USER);
 
-        $start = new \DateTime('-10 days');
+        $start = new \DateTime('-8 hours');
 
         $fixture = new TimesheetFixtures();
         $fixture
@@ -752,7 +752,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
             ->setHourlyRate(true)
             ->setAmount(0)
             ->setUser($this->getUserByRole(User::ROLE_USER))
-            ->setStartDate($start)
+            ->setFixedStartDate($start)
             ->setAmountRunning(1)
         ;
         $timesheets = $this->importFixture($fixture);
@@ -772,6 +772,30 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $this->assertInstanceOf(\DateTime::class, $timesheet->getEnd());
     }
 
+    public function testStopActionTriggersValidationOnLongRunning()
+    {
+        $client = $this->getClientForAuthenticatedUser(User::ROLE_USER);
+        $this->setSystemConfiguration('timesheet.rules.long_running_duration', 750);
+        $this->importFixtureForUser(User::ROLE_USER);
+
+        $start = new \DateTime('-13 hours');
+
+        $fixture = new TimesheetFixtures();
+        $fixture
+            ->setFixedRate(true)
+            ->setHourlyRate(true)
+            ->setAmount(0)
+            ->setUser($this->getUserByRole(User::ROLE_USER))
+            ->setFixedStartDate($start)
+            ->setAmountRunning(1)
+        ;
+        $timesheets = $this->importFixture($fixture);
+        $id = $timesheets[0]->getId();
+
+        $this->request($client, '/api/timesheets/' . $id . '/stop', 'PATCH');
+        $this->assertApiCallValidationError($client->getResponse(), ['duration' => 'Maximum 12:30 hours allowed.']);
+    }
+
     public function testStopActionFailsOnStoppedEntry()
     {
         $client = $this->getClientForAuthenticatedUser(User::ROLE_USER);
@@ -995,7 +1019,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $data = [
             'activity' => 1,
             'project' => 1,
-            'begin' => ($dateTime->createDateTime('- 16 hours'))->format('Y-m-d H:m:0'),
+            'begin' => ($dateTime->createDateTime('- 8 hours'))->format('Y-m-d H:m:0'),
             'end' => ($dateTime->createDateTime())->format('Y-m-d H:m:0'),
             'description' => 'foo',
             'fixedRate' => 2016,
@@ -1008,7 +1032,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $this->assertIsArray($result);
         self::assertApiResponseTypeStructure('TimesheetEntity', $result);
         $this->assertNotEmpty($result['id']);
-        $this->assertTrue($result['duration'] == 57600 || $result['duration'] == 57660); // 1 minute rounding might be applied
+        $this->assertTrue($result['duration'] == 28800 || $result['duration'] == 28860); // 1 minute rounding might be applied
         $this->assertEquals(2016, $result['rate']);
 
         $this->request($client, '/api/timesheets/' . $result['id'] . '/duplicate', 'PATCH');
@@ -1018,7 +1042,7 @@ class TimesheetControllerTest extends APIControllerBaseTest
         $this->assertIsArray($result);
         self::assertApiResponseTypeStructure('TimesheetEntity', $result);
         $this->assertNotEmpty($result['id']);
-        $this->assertTrue($result['duration'] == 57600 || $result['duration'] == 57660); // 1 minute rounding might be applied
+        $this->assertTrue($result['duration'] == 28800 || $result['duration'] == 28860); // 1 minute rounding might be applied
         $this->assertEquals(2016, $result['rate']);
     }
 
diff --git a/tests/Controller/TimesheetControllerTest.php b/tests/Controller/TimesheetControllerTest.php
index 0ec8c0e8..ca83126c 100644
--- a/tests/Controller/TimesheetControllerTest.php
+++ b/tests/Controller/TimesheetControllerTest.php
@@ -304,10 +304,10 @@ class TimesheetControllerTest extends ControllerBaseTest
         $this->assertEquals(50, $timesheet->getRate());
 
         $expected = new \DateTime('2018-08-02T20:00:00');
-        $this->assertEquals($expected->format(\DateTime::ATOM), $timesheet->getBegin()->format(\DateTime::ATOM));
+        $this->assertEquals($expected->format(\DateTimeInterface::ATOM), $timesheet->getBegin()->format(\DateTimeInterface::ATOM));
 
         $expected = new \DateTime('2018-08-02T20:30:00');
-        $this->assertEquals($expected->format(\DateTime::ATOM), $timesheet->getEnd()->format(\DateTime::ATOM));
+        $this->assertEquals($expected->format(\DateTimeInterface::ATOM), $timesheet->getEnd()->format(\DateTimeInterface::ATOM));
     }
 
     public function testCreateActionWithFromAndToValuesTwice()
@@ -338,10 +338,10 @@ class TimesheetControllerTest extends ControllerBaseTest
         $this->assertEquals(50, $timesheet->getRate());
 
         $expected = new \DateTime('2018-08-02T20:00:00');
-        $this->assertEquals($expected->format(\DateTime::ATOM), $timesheet->getBegin()->format(\DateTime::ATOM));
+        $this->assertEquals($expected->format(\DateTimeInterface::ATOM), $timesheet->getBegin()->format(\DateTimeInterface::ATOM));
 
         $expected = new \DateTime('2018-08-02T20:30:00');
-        $this->assertEquals($expected->format(\DateTime::ATOM), $timesheet->getEnd()->format(\DateTime::ATOM));
+        $this->assertEquals($expected->format(\DateTimeInterface::ATOM), $timesheet->getEnd()->format(\DateTimeInterface::ATOM));
 
         // create a second entry that is overlapping
         $this->request($client, '/timesheet/create?from=2018-08-02T20%3A02%3A00&to=2018-08-02T20%3A20%3A00');
@@ -489,10 +489,10 @@ class TimesheetControllerTest extends ControllerBaseTest
         $this->assertEquals(800, $timesheet->getRate());
 
         $expected = new \DateTime('2018-08-02T10:00:00');
-        $this->assertEquals($expected->format(\DateTime::ATOM), $timesheet->getBegin()->format(\DateTime::ATOM));
+        $this->assertEquals($expected->format(\DateTimeInterface::ATOM), $timesheet->getBegin()->format(\DateTimeInterface::ATOM));
 
         $expected = new \DateTime('2018-08-02T18:00:00');
-        $this->assertEquals($expected->format(\DateTime::ATOM), $timesheet->getEnd()->format(\DateTime::ATOM));
+        $this->assertEquals($expected->format(\DateTimeInterface::ATOM), $timesheet->getEnd()->format(\DateTimeInterface::ATOM));
 
         $this->assertEquals(['one', 'two', 'three'], $timesheet->getTagsAsArray());
     }
@@ -502,9 +502,9 @@ class TimesheetControllerTest extends ControllerBaseTest
         $client = $this->getClientForAuthenticatedUser();
 
         $fixture = new TimesheetFixtures();
-        $fixture->setAmount(10);
+        $fixture->setAmount(1);
         $fixture->setUser($this->getUserByRole(User::ROLE_USER));
-        $fixture->setStartDate('2017-05-01');
+        $fixture->setFixedStartDate(new \DateTime('-2 hours'));
         $timesheets = $this->importFixture($fixture);
         $id = $timesheets[0]->getId();
 
@@ -527,6 +527,10 @@ class TimesheetControllerTest extends ControllerBaseTest
             ]
         ]);
 
+        if (!$client->getResponse()->isRedirect()) {
+            dd($response->getStatusCode(), $response->getContent());
+        }
+
         $this->assertIsRedirect($client, $this->createUrl('/timesheet/'));
         $client->followRedirect();
         $this->assertTrue($client->getResponse()->isSuccessful());
@@ -645,7 +649,7 @@ class TimesheetControllerTest extends ControllerBaseTest
         $fixture->setCallback(function (Timesheet $timesheet) {
             $timesheet->setDescription('Testing is fun!');
             $end = clone $timesheet->getBegin();
-            $end->modify('+ 16 hours');
+            $end->modify('+ 8 hours');
             $timesheet->setEnd($end);
             $timesheet->setFixedRate(2016);
             $timesheet->setHourlyRate(127);
@@ -675,7 +679,7 @@ class TimesheetControllerTest extends ControllerBaseTest
         $this->assertEquals(2016, $timesheet->getRate());
         $this->assertEquals(127, $timesheet->getHourlyRate());
         $this->assertEquals(2016, $timesheet->getFixedRate());
-        $this->assertTrue($timesheet->getDuration() == 57600 || $timesheet->getDuration() == 57660); // 1 minute rounding might be applied
+        $this->assertTrue($timesheet->getDuration() == 28800 || $timesheet->getDuration() == 28860); // 1 minute rounding might be applied
         $this->assertEquals(2016, $timesheet->getRate());
     }
 }
diff --git a/tests/Controller/TimesheetTeamControllerTest.php b/tests/Controller/TimesheetTeamControllerTest.php
index f30af226..c7f00848 100644
--- a/tests/Controller/TimesheetTeamControllerTest.php
+++ b/tests/Controller/TimesheetTeamControllerTest.php
@@ -265,13 +265,12 @@ class TimesheetTeamControllerTest extends ControllerBaseTest
     {
         $client = $this->getClientForAuthenticatedUser(User::ROLE_ADMIN);
 
-        $em = $this->getEntityManager();
         $user = $this->getUserByRole(User::ROLE_USER);
         $teamlead = $this->getUserByRole(User::ROLE_TEAMLEAD);
         $fixture = new TimesheetFixtures();
         $fixture->setAmount(10);
         $fixture->setUser($user);
-        $fixture->setStartDate('2017-05-01');
+        $fixture->setFixedStartDate(new \DateTime('-2 hours'));
         $timesheets = $this->importFixture($fixture);
         $id = $timesheets[0]->getId();
 
@@ -420,7 +419,7 @@ class TimesheetTeamControllerTest extends ControllerBaseTest
         $fixture->setCallback(function (Timesheet $timesheet) {
             $timesheet->setDescription('Testing is fun!');
             $end = clone $timesheet->getBegin();
-            $end->modify('+ 16 hours');
+            $end->modify('+ 8 hours');
             $timesheet->setEnd($end);
             $timesheet->setFixedRate(2016);
             $timesheet->setHourlyRate(127);
@@ -450,7 +449,7 @@ class TimesheetTeamControllerTest extends ControllerBaseTest
         $this->assertEquals(2016, $timesheet->getRate());
         $this->assertEquals(127, $timesheet->getHourlyRate());
         $this->assertEquals(2016, $timesheet->getFixedRate());
-        $this->assertTrue($timesheet->getDuration() == 57600 || $timesheet->getDuration() == 57660); // 1 minute rounding might be applied
+        $this->assertTrue($timesheet->getDuration() == 28800 || $timesheet->getDuration() == 28860); // 1 minute rounding might be applied
         $this->assertEquals(2016, $timesheet->getRate());
     }
 }
diff --git a/tests/DataFixtures/TimesheetFixtures.php b/tests/DataFixtures/TimesheetFixtures.php
index c26b4edc..1fe6c566 100644
--- a/tests/DataFixtures/TimesheetFixtures.php
+++ b/tests/DataFixtures/TimesheetFixtures.php
@@ -48,6 +48,10 @@ final class TimesheetFixtures implements TestFixture
      * @var \DateTime
      */
     private $startDate;
+    /**
+     * @var \DateTime
+     */
+    private $fixedStartDate;
     /**
      * @var bool
      */
@@ -129,6 +133,13 @@ final class TimesheetFixtures implements TestFixture
         return $this;
     }
 
+    public function setFixedStartDate(\DateTime $date): TimesheetFixtures
+    {
+        $this->fixedStartDate = $date;
+
+        return $this;
+    }
+
     public function setAmountRunning(int $amount): TimesheetFixtures
     {
         $this->running = $amount;
@@ -312,6 +323,10 @@ final class TimesheetFixtures implements TestFixture
 
     private function getDateTime(int $i): \DateTime
     {
+        if ($this->fixedStartDate !== null) {
+            return $this->fixedStartDate;
+        }
+
         if ($this->startDate === null) {
             $this->startDate = new \DateTime('2018-04-01');
         }
diff --git a/tests/DependencyInjection/AppExtensionTest.php b/tests/DependencyInjection/AppExtensionTest.php
index f7318e14..2dc22b99 100644
--- a/tests/DependencyInjection/AppExtensionTest.php
+++ b/tests/DependencyInjection/AppExtensionTest.php
@@ -204,6 +204,8 @@ class AppExtensionTest extends TestCase
                     'lockdown_grace_period' => null,
                     'allow_overbooking_budget' => true,
                     'lockdown_period_timezone' => null,
+                    'break_warning_duration' => 0,
+                    'long_running_duration' => 0,
                 ],
                 'default_begin' => 'now',
                 'duration_increment' => null,
diff --git a/tests/DependencyInjection/ConfigurationTest.php b/tests/DependencyInjection/ConfigurationTest.php
index 5c16775f..4c40d832 100644
--- a/tests/DependencyInjection/ConfigurationTest.php
+++ b/tests/DependencyInjection/ConfigurationTest.php
@@ -289,6 +289,8 @@ class ConfigurationTest extends TestCase
                     'lockdown_grace_period' => null,
                     'allow_overbooking_budget' => true,
                     'lockdown_period_timezone' => null,
+                    'break_warning_duration' => 0,
+                    'long_running_duration' => 0,
                 ],
                 'duration_increment' => null,
                 'time_increment' => null,
diff --git a/tests/Validator/Constraints/TimesheetLongRunningValidatorTest.php b/tests/Validator/Constraints/TimesheetLongRunningValidatorTest.php
new file mode 100644
index 00000000..4d18cf20
--- /dev/null
+++ b/tests/Validator/Constraints/TimesheetLongRunningValidatorTest.php
@@ -0,0 +1,117 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Tests\Validator\Constraints;
+
+use App\Configuration\ConfigLoaderInterface;
+use App\Configuration\SystemConfiguration;
+use App\Entity\Timesheet;
+use App\Validator\Constraints\TimesheetLongRunning;
+use App\Validator\Constraints\TimesheetLongRunningValidator;
+use Symfony\Component\Validator\Constraints\NotBlank;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+use Symfony\Component\Validator\Test\ConstraintValidatorTestCase;
+
+/**
+ * @covers \App\Validator\Constraints\TimesheetLongRunningValidator
+ */
+class TimesheetLongRunningValidatorTest extends ConstraintValidatorTestCase
+{
+    protected function createValidator()
+    {
+        return $this->createMyValidator(120);
+    }
+
+    protected function createMyValidator(int $minutes)
+    {
+        $loader = $this->createMock(ConfigLoaderInterface::class);
+        $config = new SystemConfiguration($loader, [
+            'timesheet' => [
+                'rules' => [
+                    'long_running_duration' => $minutes,
+                ],
+            ],
+        ]);
+
+        return new TimesheetLongRunningValidator($config);
+    }
+
+    public function testConstraintIsInvalid()
+    {
+        $this->expectException(UnexpectedTypeException::class);
+
+        $this->validator->validate(new Timesheet(), new NotBlank());
+    }
+
+    public function testInvalidValueThrowsException()
+    {
+        $this->expectException(UnexpectedTypeException::class);
+
+        $this->validator->validate(new NotBlank(), new TimesheetLongRunning(['message' => 'myMessage']));
+    }
+
+    public function testLongRunningTriggers()
+    {
+        $begin = new \DateTime();
+        $end = new \DateTime('+10 hour');
+        $timesheet = new Timesheet();
+        $timesheet->setBegin($begin);
+        $timesheet->setEnd($end);
+
+        $this->validator->validate($timesheet, new TimesheetLongRunning());
+
+        $this->buildViolation('Maximum duration of {{ value }} hours exceeded.')
+            ->atPath('property.path.duration')
+            ->setParameter('{{ value }}', '02:00')
+            ->setCode(TimesheetLongRunning::LONG_RUNNING)
+            ->assertRaised();
+    }
+
+    public function testLongRunningNotTriggersIfConfiguredToZero()
+    {
+        $this->validator = $this->createMyValidator(0);
+        $this->validator->initialize($this->context);
+
+        $begin = new \DateTime();
+        $end = new \DateTime('+10 hour');
+        $timesheet = new Timesheet();
+        $timesheet->setBegin($begin);
+        $timesheet->setEnd($end);
+
+        $this->validator->validate($timesheet, new TimesheetLongRunning());
+
+        $this->assertNoViolation();
+    }
+
+    public function testLongRunningNotTriggersIfDurationIsLowerThan()
+    {
+        $this->validator = $this->createMyValidator(121);
+        $this->validator->initialize($this->context);
+
+        $begin = new \DateTime();
+        $end = new \DateTime('+2 hour');
+        $timesheet = new Timesheet();
+        $timesheet->setBegin($begin);
+        $timesheet->setEnd($end);
+
+        $this->validator->validate($timesheet, new TimesheetLongRunning());
+
+        $this->assertNoViolation();
+    }
+
+    public function testNotTriggersOnRunningRecord()
+    {
+        $begin = new \DateTime('-10 hour');
+        $timesheet = new Timesheet();
+        $timesheet->setBegin($begin);
+
+        $this->validator->validate($timesheet, new TimesheetLongRunning());
+        $this->assertNoViolation();
+    }
+}
diff --git a/translations/system-configuration.de.xlf b/translations/system-configuration.de.xlf
index 196f0227..545a333e 100644
--- a/translations/system-configuration.de.xlf
+++ b/translations/system-configuration.de.xlf
@@ -298,6 +298,14 @@
         <source>label.saml_activate</source>
         <target>SAML Anmeldung</target>
       </trans-unit>
+      <trans-unit id="label.timesheet.rules.break_warning_duration">
+        <source>label.timesheet.rules.break_warning_duration</source>
+        <target>Maximale Dauer eines Zeiteintrags in Minuten, bevor eine Pausen-Warnung angezeigt wird (0 = deaktiviert)</target>
+      </trans-unit>
+      <trans-unit id="label.timesheet.rules.long_running_duration">
+        <source>label.timesheet.rules.long_running_duration</source>
+        <target>Maximale Dauer eines Zeiteintrags in Minuten, bevor das Speichern abgelehnt wird (0 = deaktiviert)</target>
+      </trans-unit>
     </body>
   </file>
 </xliff>
diff --git a/translations/system-configuration.en.xlf b/translations/system-configuration.en.xlf
index a2304f4a..1b37eae3 100644
--- a/translations/system-configuration.en.xlf
+++ b/translations/system-configuration.en.xlf
@@ -298,6 +298,14 @@
                 <source>label.saml_activate</source>
                 <target>SAML login</target>
             </trans-unit>
+            <trans-unit id="label.timesheet.rules.break_warning_duration">
+                <source>label.timesheet.rules.break_warning_duration</source>
+                <target>Maximum duration of a timesheet record in minutes before a "break warning" will be displayed (0 = deactivated)</target>
+            </trans-unit>
+            <trans-unit id="label.timesheet.rules.long_running_duration">
+                <source>label.timesheet.rules.long_running_duration</source>
+                <target>Maximum duration of a timesheet record in minutes before saving is rejected (0 = deactivated)</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/translations/validators.de.xlf b/translations/validators.de.xlf
index 561cd1b1..04d048cf 100644
--- a/translations/validators.de.xlf
+++ b/translations/validators.de.xlf
@@ -50,6 +50,10 @@
                 <source>The budget is completely used.</source>
                 <target>Das Budget ist aufgebraucht. Von den vorhandenen %budget% wurden bisher %used% gebucht, noch nutzbar sind %free%.</target>
             </trans-unit>
+            <trans-unit id="Maximum duration of {{ value }} hours exceeded.">
+                <source>Maximum duration of {{ value }} hours exceeded.</source>
+                <target>Erlaubt sind max. {{ value }} Stunden.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/translations/validators.en.xlf b/translations/validators.en.xlf
index 5524f9d6..5cf91f4f 100644
--- a/translations/validators.en.xlf
+++ b/translations/validators.en.xlf
@@ -50,6 +50,10 @@
                 <source>The budget is completely used.</source>
                 <target>The budget is used up. Of the available %budget%, %used% has been booked so far, %free% can still be used.</target>
             </trans-unit>
+            <trans-unit id="Maximum duration of {{ value }} hours exceeded.">
+                <source>Maximum duration of {{ value }} hours exceeded.</source>
+                <target>Maximum {{ value }} hours allowed.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>