diff --git a/database/factories/TimeEntryFactory.php b/database/factories/TimeEntryFactory.php
index 2bb83514..1a1fd5d2 100644
--- a/database/factories/TimeEntryFactory.php
+++ b/database/factories/TimeEntryFactory.php
@@ -147,8 +147,8 @@ class TimeEntryFactory extends Factory
     {
         return $this->state(function (array $attributes) use ($start, $durationInSeconds): array {
             return [
-                'start' => $start->utc(),
-                'end' => $start->copy()->addSeconds($durationInSeconds),
+                'start' => $start->copy()->utc(),
+                'end' => $start->copy()->utc()->addSeconds($durationInSeconds),
             ];
         });
     }
@@ -157,7 +157,7 @@ class TimeEntryFactory extends Factory
     {
         return $this->state(function (array $attributes) use ($start): array {
             return [
-                'start' => $start->utc(),
+                'start' => $start->copy()->utc(),
             ];
         });
     }
diff --git a/tests/TestCase.php b/tests/TestCase.php
index ad6ba8dd..c246269d 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -31,6 +31,8 @@ abstract class TestCase extends BaseTestCase
             $mock->shouldReceive('getTrialUntil')->andReturn(null);
             $mock->shouldReceive('isBlocked')->andReturn(false);
         });
+        // Note: The following line can be used to test timezone edge cases.
+        // $this->travelTo(Carbon::now()->timezone('Europe/Vienna')->setHour(0)->setMinute(59)->setSecond(0));
     }
 
     protected function mockPrivateStorage(): void
diff --git a/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php b/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
index ec7d3883..c715e358 100644
--- a/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
+++ b/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
@@ -473,8 +473,8 @@ class TimeEntryEndpointTest extends ApiEndpointTestAbstract
             'time-entries:view:all',
         ]);
         $project = Project::factory()->forOrganization($data->organization)->create();
-        $day1 = Carbon::now()->timezone($data->user->timezone)->subDays(1)->utc();
-        $day2 = Carbon::now()->timezone($data->user->timezone)->subDays(3)->utc();
+        $day1 = Carbon::now()->timezone($data->user->timezone)->subDays(1);
+        $day2 = Carbon::now()->timezone($data->user->timezone)->subDays(3);
         $timeEntry1NoProject = TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->startWithDuration($day1, 10)->create();
         $timeEntry2NoProject = TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->startWithDuration($day2, 10)->create();
         $timeEntry1WithProject = TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->forProject($project)->startWithDuration($day1, 10)->create();
@@ -552,8 +552,8 @@ class TimeEntryEndpointTest extends ApiEndpointTestAbstract
             'time-entries:view:all',
         ]);
         $project = Project::factory()->forOrganization($data->organization)->create();
-        $day1 = Carbon::now()->timezone($data->user->timezone)->subDays(1)->utc();
-        $day2 = Carbon::now()->timezone($data->user->timezone)->subDays(3)->utc();
+        $day1 = Carbon::now()->timezone($data->user->timezone)->subDays(1);
+        $day2 = Carbon::now()->timezone($data->user->timezone)->subDays(3);
         $timeEntry1NoProject = TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->startWithDuration($day1, 10)->create();
         $timeEntry2NoProject = TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->startWithDuration($day2, 10)->create();
         $timeEntry1WithProject = TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->forProject($project)->startWithDuration($day1, 10)->create();
diff --git a/tests/Unit/Service/TimeEntryAggregationServiceTest.php b/tests/Unit/Service/TimeEntryAggregationServiceTest.php
index c9974b41..65487b47 100644
--- a/tests/Unit/Service/TimeEntryAggregationServiceTest.php
+++ b/tests/Unit/Service/TimeEntryAggregationServiceTest.php
@@ -140,6 +140,7 @@ class TimeEntryAggregationServiceTest extends TestCaseWithDatabase
     public function test_aggregate_time_entries_empty_state_by_day_and_project_with_filled_gaps(): void
     {
         // Arrange
+        $timezone = 'Europe/Vienna';
         $query = TimeEntry::query();
 
         // Act
@@ -147,7 +148,7 @@ class TimeEntryAggregationServiceTest extends TestCaseWithDatabase
             $query,
             TimeEntryAggregationType::Day,
             TimeEntryAggregationType::Project,
-            'Europe/Vienna',
+            $timezone,
             Weekday::Monday,
             true,
             Carbon::now()->subDays(2)->utc(),
@@ -161,14 +162,14 @@ class TimeEntryAggregationServiceTest extends TestCaseWithDatabase
             'grouped_type' => 'day',
             'grouped_data' => [
                 [
-                    'key' => Carbon::now()->subDays(2)->utc()->format('Y-m-d'),
+                    'key' => Carbon::now()->subDays(2)->timezone($timezone)->format('Y-m-d'),
                     'seconds' => 0,
                     'cost' => 0,
                     'grouped_type' => 'project',
                     'grouped_data' => [],
                 ],
                 [
-                    'key' => Carbon::now()->subDay()->utc()->format('Y-m-d'),
+                    'key' => Carbon::now()->subDay()->timezone($timezone)->format('Y-m-d'),
                     'seconds' => 0,
                     'cost' => 0,
                     'grouped_type' => 'project',