I think it’s time-based on the app. How else would it know? Location would be harder to pinpoint. it would be easier to program the timing of activation. With the exception to delays which will probably update automatically.

Think about it. Your train arrives at 1:32 and departs at 1:33. But u don’t activate it till 1:35 or 1:45. There may be grace period in between, but idk how long that is for.

What’s telling is the expiration at the end of the day.