diff --git a/launch.html b/launch.html
index 8336b8b..c5c89bb 100644
--- a/launch.html
+++ b/launch.html
@@ -460,12 +460,12 @@
           
           <div class="form-group">
             <label for="meetingStart" data-i18n="creator.meetingStartLabel">Start Date & Time</label>
-            <input type="datetime-local" id="meetingStart" />
+            <input type="datetime-local" id="meetingStart" step="900" />
           </div>
-          
+
           <div class="form-group">
             <label for="meetingEnd" data-i18n="creator.meetingEndLabel">End Date & Time</label>
-            <input type="datetime-local" id="meetingEnd" />
+            <input type="datetime-local" id="meetingEnd" step="900" />
           </div>
           
           <div class="form-group">
@@ -1422,6 +1422,51 @@ END:VCALENDAR`;
         return url;
       }
 
+      const MINUTES_STEP = 15;
+      const DEFAULT_DURATION_MINUTES = 30;
+
+      /*
+       * Minuten auf das 15-Minuten-Raster aufrunden.
+       *
+       * Beispiel:
+       *
+       * 14:07 ergibt 14:15
+       * 14:50 ergibt 15:00
+       */
+      function roundMinutes(date) {
+        const rounded = new Date(date);
+
+        rounded.setSeconds(0, 0);
+        rounded.setMinutes(
+          Math.ceil(date.getMinutes() / MINUTES_STEP) * MINUTES_STEP
+        );
+
+        return rounded;
+      }
+
+      /*
+       * Lokale Zeit für datetime-local formatieren.
+       *
+       * Beispiel:
+       *
+       * 1. Januar 2026, 14:15 ergibt "2026-01-01T14:15"
+       */
+      function formatLocal(date) {
+        const pad = (num) => num.toString().padStart(2, "0");
+
+        return (
+          date.getFullYear() +
+          "-" +
+          pad(date.getMonth() + 1) +
+          "-" +
+          pad(date.getDate()) +
+          "T" +
+          pad(date.getHours()) +
+          ":" +
+          pad(date.getMinutes())
+        );
+      }
+
       function showMeetingCreator() {
         /* Hide all other views */
         launcher.classList.add("hidden");
@@ -1441,11 +1486,13 @@ END:VCALENDAR`;
         icsSuccess.classList.add("hidden");
         
         /* Set default start and end times */
-        const now = new Date();
-        const inOneHour = new Date(now.getTime() + 60 * 60 * 1000);
-        
-        meetingStartInput.value = now.toISOString().slice(0, 16);
-        meetingEndInput.value = inOneHour.toISOString().slice(0, 16);
+        const start = roundMinutes(new Date());
+        const end = new Date(
+          start.getTime() + DEFAULT_DURATION_MINUTES * 60 * 1000
+        );
+
+        meetingStartInput.value = formatLocal(start);
+        meetingEndInput.value = formatLocal(end);
       }
 
       function createMeeting() {