minus method
Returns a new LocalTime with the given duration
subtracted.
If the result is negative, it wraps backward from the end of the day.
Example
final t = LocalTime(0, 15);
final prev = t.minus(Duration(minutes: 30)); // 23:45 of previous cycle
Implementation
LocalTime minus(Duration duration) {
final totalMilliseconds = toMillisecondOfDay() - duration.inMilliseconds;
final normalized = (totalMilliseconds % _dayMilliseconds + _dayMilliseconds) % _dayMilliseconds;
return LocalTime.fromMillisecondOfDay(normalized);
}