Fixed issue with a specific string as initial duration

lib/widgets/duration_picker.dart

@@ -26,7 +26,7 @@ class _DurationPickerState extends State<DurationPicker> {
     super.initState();
     if (widget.initialDuration.inMinutes != 0) {
       _timeString =
-          '${widget.initialDuration.inHours}${widget.initialDuration.inMinutes % 60}';
+          '${widget.initialDuration.inHours}${(widget.initialDuration.inMinutes % 60).toString().padLeft(2, '0')}';
     }
   }