diff --git a/src/Controller/SystemConfigurationController.php b/src/Controller/SystemConfigurationController.php
index ffbaf1ab..50d7cedb 100644
--- a/src/Controller/SystemConfigurationController.php
+++ b/src/Controller/SystemConfigurationController.php
@@ -14,12 +14,14 @@ use App\Event\SystemConfigurationEvent;
 use App\Form\Model\Configuration;
 use App\Form\Model\SystemConfiguration as SystemConfigurationModel;
 use App\Form\SystemConfigurationForm;
+use App\Form\Type\DateTimeTextType;
 use App\Form\Type\LanguageType;
 use App\Form\Type\RoundingModeType;
 use App\Form\Type\SkinType;
 use App\Form\Type\TrackingModeType;
 use App\Form\Type\WeekDaysType;
 use App\Repository\ConfigurationRepository;
+use App\Validator\Constraints\DateTimeFormat;
 use Sensio\Bundle\FrameworkExtraBundle\Configuration\Security;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\Form\Extension\Core\Type\CheckboxType;
@@ -216,6 +218,11 @@ final class SystemConfigurationController extends AbstractController
                         ->setName('timesheet.mode')
                         ->setType(TrackingModeType::class)
                         ->setTranslationDomain('system-configuration'),
+                    (new Configuration())
+                        ->setName('timesheet.default_begin')
+                        ->setType(DateTimeTextType::class)
+                        ->setConstraints([new DateTimeFormat(), new NotNull()])
+                        ->setTranslationDomain('system-configuration'),
                     (new Configuration())
                         ->setName('timesheet.rules.allow_future_times')
                         ->setType(CheckboxType::class)
diff --git a/src/Form/Type/DateTimeTextType.php b/src/Form/Type/DateTimeTextType.php
new file mode 100644
index 00000000..58939e71
--- /dev/null
+++ b/src/Form/Type/DateTimeTextType.php
@@ -0,0 +1,24 @@
+<?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\Form\Type;
+
+use Symfony\Component\Form\AbstractType;
+use Symfony\Component\Form\Extension\Core\Type\TextType;
+
+class DateTimeTextType extends AbstractType
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getParent()
+    {
+        return TextType::class;
+    }
+}
diff --git a/src/Validator/Constraints/DateTimeFormat.php b/src/Validator/Constraints/DateTimeFormat.php
new file mode 100644
index 00000000..986fba23
--- /dev/null
+++ b/src/Validator/Constraints/DateTimeFormat.php
@@ -0,0 +1,28 @@
+<?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 Symfony\Component\Validator\Constraint;
+
+class DateTimeFormat extends Constraint
+{
+    public const INVALID_FORMAT = 'kimai-datetime-00';
+
+    protected static $errorNames = [
+        self::INVALID_FORMAT => 'The given value is not a valid datetime format.',
+    ];
+
+    public $message = 'This datetime format is invalid.';
+
+    public function getTargets()
+    {
+        return self::PROPERTY_CONSTRAINT;
+    }
+}
diff --git a/src/Validator/Constraints/DateTimeFormatValidator.php b/src/Validator/Constraints/DateTimeFormatValidator.php
new file mode 100644
index 00000000..7e179713
--- /dev/null
+++ b/src/Validator/Constraints/DateTimeFormatValidator.php
@@ -0,0 +1,43 @@
+<?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 Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+
+class DateTimeFormatValidator extends ConstraintValidator
+{
+    /**
+     * @param string|mixed $value
+     * @param Constraint $constraint
+     */
+    public function validate($value, Constraint $constraint)
+    {
+        if (!($constraint instanceof DateTimeFormat)) {
+            throw new UnexpectedTypeException($constraint, __NAMESPACE__ . '\DateTimeFormat');
+        }
+
+        $valid = true;
+
+        try {
+            $test = new \DateTime($value);
+        } catch (\Exception $ex) {
+            $valid = false;
+        }
+
+        if (false === $valid) {
+            $this->context->buildViolation('The given value is not a valid datetime format.')
+                ->setTranslationDomain('validators')
+                ->setCode(DateTimeFormat::INVALID_FORMAT)
+                ->addViolation();
+        }
+    }
+}
diff --git a/tests/Controller/SystemConfigurationControllerTest.php b/tests/Controller/SystemConfigurationControllerTest.php
index e95237c0..240a959a 100644
--- a/tests/Controller/SystemConfigurationControllerTest.php
+++ b/tests/Controller/SystemConfigurationControllerTest.php
@@ -93,6 +93,7 @@ class SystemConfigurationControllerTest extends ControllerBaseTest
             'system_configuration_form_timesheet' => [
                 'configuration' => [
                     ['name' => 'timesheet.mode', 'value' => 'duration_only'],
+                    ['name' => 'timesheet.active_entries.default_begin', 'value' => '23:59'],
                     ['name' => 'timesheet.rules.allow_future_times', 'value' => false],
                     ['name' => 'timesheet.active_entries.hard_limit', 'value' => 99],
                     ['name' => 'timesheet.active_entries.soft_limit', 'value' => 77],
@@ -122,6 +123,7 @@ class SystemConfigurationControllerTest extends ControllerBaseTest
                 'system_configuration_form_timesheet' => [
                     'configuration' => [
                         ['name' => 'timesheet.mode', 'value' => 'foo'],
+                        ['name' => 'timesheet.active_entries.default_begin', 'value' => '23:59'],
                         ['name' => 'timesheet.rules.allow_future_times', 'value' => 1],
                         ['name' => 'timesheet.active_entries.hard_limit', 'value' => -1],
                         ['name' => 'timesheet.active_entries.soft_limit', 'value' => -1],
@@ -130,8 +132,8 @@ class SystemConfigurationControllerTest extends ControllerBaseTest
             ],
             [
                 '#system_configuration_form_timesheet_configuration_0_value', // mode
-                '#system_configuration_form_timesheet_configuration_2_value', // hard_limit
-                '#system_configuration_form_timesheet_configuration_3_value', // soft_limit
+                '#system_configuration_form_timesheet_configuration_3_value', // hard_limit
+                '#system_configuration_form_timesheet_configuration_4_value', // soft_limit
             ],
             true
         );
diff --git a/tests/Validator/Constraints/DateTimeFormatValidatorTest.php b/tests/Validator/Constraints/DateTimeFormatValidatorTest.php
new file mode 100644
index 00000000..bf6b2c25
--- /dev/null
+++ b/tests/Validator/Constraints/DateTimeFormatValidatorTest.php
@@ -0,0 +1,85 @@
+<?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\Validator\Constraints\DateTimeFormat;
+use App\Validator\Constraints\DateTimeFormatValidator;
+use Symfony\Component\Validator\Constraints\NotBlank;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+use Symfony\Component\Validator\Test\ConstraintValidatorTestCase;
+
+/**
+ * @covers \App\Validator\Constraints\DateTimeFormatValidator
+ */
+class DateTimeFormatValidatorTest extends ConstraintValidatorTestCase
+{
+    protected function createValidator()
+    {
+        return new DateTimeFormatValidator();
+    }
+
+    public function getValidData()
+    {
+        return [
+            ['10:00'],
+            ['now'],
+            ['2020-12-31 13:31:29'],
+            ['monday this week 12:44'],
+            [''], // empty is now
+            [null], // null is now
+        ];
+    }
+
+    public function testConstraintIsInvalid()
+    {
+        $this->expectException(UnexpectedTypeException::class);
+
+        $this->validator->validate('foo', new NotBlank());
+    }
+
+    /**
+     * @dataProvider getValidData
+     * @param string $input
+     */
+    public function testConstraintWithValidData($input)
+    {
+        $constraint = new DateTimeFormat();
+        $this->validator->validate($input, $constraint);
+        $this->assertNoViolation();
+    }
+
+    public function getInvalidData()
+    {
+        return [
+            ['13-13'],
+            ['3127::00'],
+            ['3127:00:'],
+            [':3127:00'],
+            ['::3127'],
+        ];
+    }
+
+    /**
+     * @dataProvider getInvalidData
+     * @param mixed $input
+     */
+    public function testValidationError($input)
+    {
+        $constraint = new DateTimeFormat();
+
+        $this->validator->validate($input, $constraint);
+
+        $expectedFormat = is_string($input) ? '"' . $input . '"' : $input;
+
+        $this->buildViolation('The given value is not a valid datetime format.')
+            ->setCode(DateTimeFormat::INVALID_FORMAT)
+            ->assertRaised();
+    }
+}
diff --git a/translations/system-configuration.de.xlf b/translations/system-configuration.de.xlf
index f7ac9b4b..ade9f5aa 100644
--- a/translations/system-configuration.de.xlf
+++ b/translations/system-configuration.de.xlf
@@ -190,6 +190,10 @@
                 <source>Floor</source>
                 <target>Floor: Start, Ende und Dauer werden nach unten gerundet</target>
             </trans-unit>
+            <trans-unit id="label.timesheet.default_begin">
+                <source>label.timesheet.default_begin</source>
+                <target>Standard Startzeit (wird nicht in jedem Zeiterfassungs Modus verwendet)</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/translations/system-configuration.en.xlf b/translations/system-configuration.en.xlf
index 2d1d1532..011529b1 100644
--- a/translations/system-configuration.en.xlf
+++ b/translations/system-configuration.en.xlf
@@ -190,6 +190,10 @@
                 <source>Floor</source>
                 <target>Floor: begin, end and duration will be rounded down</target>
             </trans-unit>
+            <trans-unit id="label.timesheet.default_begin">
+                <source>label.timesheet.default_begin</source>
+                <target>Default start-time (not used in all timetracking modes)</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>