This goes back to the discussion of cycle times that s8film40 talked about. Not all of the timers work properly, but when they sense a train in the station, it starts to count up to calculate the station time. Ideally a station time should be around 90 seconds. When the train clears the station, the time resets to zero (or pauses and resets when another train pulls in - I can't remember). When I was there, they tried to turn those timers off because the management wanted to do away with cycle times. For whatever reason, they were under the impression that pilots would put lap times before safety. So going back to your original question, there is no pattern as they are now irrelevant.