Added api for custom timetable events

lib/extensions/dateTime.dart

@@ -1,3 +1,5 @@
+import 'package:flutter/material.dart';
+
 extension IsSameDay on DateTime {
   bool isSameDay(DateTime other) {
     return year == other.year && month == other.month && day == other.day;
@@ -6,4 +8,12 @@ extension IsSameDay on DateTime {
   DateTime nextWeekday(int day) {
     return add(Duration(days: (day - weekday) % DateTime.daysPerWeek));
   }
+
+  DateTime withTime(TimeOfDay time) {
+    return copyWith(hour: time.hour, minute: time.minute);
+  }
+
+  TimeOfDay toTimeOfDay() {
+    return TimeOfDay(hour: hour, minute: minute);
+  }
 }