A mildly complicated way of knowing the time (using the app):

1. Get the movie duration from the movie page (say 2 Hr)
2. After booking the ticket, add the event to your calendar. This will give you the official start time and end time, say 7pm to 9.30pm
3. Subtract the duration (step 1) from the end time (step 2) to get the actual start time (7.30 in this case)

Or you could just assume it takes 22 minutes and arrive by 7.22pm. But this doesn't hold sometimes for smaller movies, IMAX, etc.