Returns a new TimeOfDay with the hour and/or minute replaced.
Source
TimeOfDay replacing({ int hour, int minute }) {
assert(hour == null || (hour >= 0 && hour < _kHoursPerDay));
assert(minute == null || (minute >= 0 && minute < _kMinutesPerHour));
return new TimeOfDay(hour: hour ?? this.hour, minute: minute ?? this.minute);
}