diff --git a/includes/view/ShiftCalendarRenderer.php b/includes/view/ShiftCalendarRenderer.php
index ad8542bc..387b911d 100644
--- a/includes/view/ShiftCalendarRenderer.php
+++ b/includes/view/ShiftCalendarRenderer.php
@@ -2,6 +2,7 @@
 
 namespace Engelsystem;
 
+use Engelsystem\Helpers\Carbon;
 use Engelsystem\Models\Shifts\Shift;
 use Engelsystem\Models\Shifts\ShiftEntry;
 use Illuminate\Support\Collection;
@@ -212,20 +213,21 @@ class ShiftCalendarRenderer
      */
     private function renderTick($time, $label = false)
     {
+        $time = Carbon::createFromTimestamp($time);
         $class = $label ? 'tick bg-' . theme_type() : 'tick ';
-        if ($time % (24 * 60 * 60) == 23 * 60 * 60) {
+        if ($time->isStartOfDay()) {
             if (!$label) {
                 return div($class . ' day');
             }
             return div($class . ' day', [
-                date(__('m-d'), $time) . '<br>' . date(__('H:i'), $time),
+                $time->format(__('m-d')) . '<br>' . $time->format(__('H:i')),
             ]);
-        } elseif ($time % (60 * 60) == 0) {
+        } elseif ($time->isStartOfHour()) {
             if (!$label) {
                 return div($class . ' hour');
             }
             return div($class . ' hour', [
-                date(__('m-d'), $time) . '<br>' . date(__('H:i'), $time),
+                $time->format(__('m-d')) . '<br>' . $time->format(__('H:i')),
             ]);
         }
         return div($class);
diff --git a/src/Helpers/Carbon.php b/src/Helpers/Carbon.php
index c12747f5..931a74a8 100644
--- a/src/Helpers/Carbon.php
+++ b/src/Helpers/Carbon.php
@@ -18,7 +18,7 @@ class Carbon extends \Carbon\Carbon
     /**
      * Parses HTML datetime-local and ISO date/time strings.
      *
-     * @return \Carbon\Carbon|null Carbon if parseable, else null
+     * @return self|null Carbon if parseable, else null
      * @see self::DATETIME_FORMATS
      */
     public static function createFromDatetime(string $value): ?\Carbon\Carbon
@@ -43,4 +43,16 @@ class Carbon extends \Carbon\Carbon
         $carbon = self::createFromDateTime($value);
         return $carbon === null ? null : $carbon->timestamp;
     }
+
+    /**
+     * Check if the instance is at the start of an hour.
+     *
+     * @param bool $checkMicroseconds check time at microseconds precision
+     */
+    public function isStartOfHour(bool $checkMicroseconds = false): bool
+    {
+        return $checkMicroseconds
+            ? $this->rawFormat('i:s.u') === '00:00.000000'
+            : $this->rawFormat('i:s') === '00:00';
+    }
 }
diff --git a/tests/Unit/Helpers/CarbonTest.php b/tests/Unit/Helpers/CarbonTest.php
index 3566dd81..d1d8b308 100644
--- a/tests/Unit/Helpers/CarbonTest.php
+++ b/tests/Unit/Helpers/CarbonTest.php
@@ -65,4 +65,28 @@ class CarbonTest extends TestCase
         $timestamp = Carbon::createTimestampFromDatetime($value);
         self::assertNull($timestamp);
     }
+
+    public function startOfHourDates(): array
+    {
+        return [
+            ['2022-04-16 10:00:00.000000', true],
+            ['2022-04-16 10:00:00.000000', true, true],
+            ['2022-04-16 10:00:00.123456', true, false],
+            ['2022-04-16 23:00:00.000000', true, false],
+            ['2022-04-16 10:00:42.000000', false],
+            ['2022-04-16 10:23:00.000000', false],
+            ['2022-04-16 10:00:00.123456', false, true],
+        ];
+    }
+
+    /**
+     * @covers       \Engelsystem\Helpers\Carbon::isStartOfHour
+     * @dataProvider startOfHourDates
+     */
+    public function testIsStartOfHour(string $value, bool $expected, bool $checkMicroseconds = false): void
+    {
+        $date = Carbon::createFromFormat('Y-m-d H:i:s.u', $value);
+
+        $this->assertEquals($expected, $date->isStartOfHour($checkMicroseconds));
+    }
 }