stopTimeUpdate.arrival: Arrival time (specified in StopTimeEvent) should be before the departure time for the same stop if a layover or dwell time is expected - otherwise, arrival time should be be the same as departure time.
Within the same stop_time_update, arrival and departures times can be the same, or the departure time can be later than the arrival time - the departure time should never come before the arrival time.
Relevant Best Practice text:
E025 text: