Handy little util for calculating time intervals between two DateTime in Dart.

date-interval.dart

void main() {
 calculateDateInterval(DateTime(2020, 09, 22, 11, 00), DateTime(2020, 09, 22, 16, 00), 0.75);
}

void calculateDateInterval(
  final DateTime startTime,
  final DateTime endTime,
  final double intervalInHours,
) {
  final workingHours = endTime.difference(startTime).inHours;
  const milliSecondsInHour = 3600000;

  final interval = (intervalInHours * milliSecondsInHour).round();
  final workingDayInMilliseconds = workingHours * milliSecondsInHour;
  final avaibleTimeSlots = (workingDayInMilliseconds ~/ interval);

final slots = <String>[];
  for (var offset = 1; offset < avaibleTimeSlots; offset++) {
    final timeOffset = startTime.millisecondsSinceEpoch + (offset * interval);
    slots.add(DateTime.fromMillisecondsSinceEpoch(timeOffset).toString());
  }
  print(slots);
}