A purchased pass will expire when:
The duration of the pass is met (1 day, 7 days, 30 days, etc.)
The number of rides provided by the pass is met
Once either of the above conditions has been met, the pass will expire. Don't worry! You can always purchase another pass by navigating to the Passes page from your menu.
Keep track of the amount of rides/duration of an active pass by navigating to Passes from the menu.
The duration/days remaining on your pass is also displayed on the main page of the app.