Decent idea but don't cinemas normally frown on people using phones during a film?
That said, the app had a "low key" design so it doesn't shine bright in the theater. ( Theoretically anyway).
When the movie starts you start the timer, and put the phone in your pocket. The the phone vibrates when a pee-time comes up. You don't have to take out your phone [until you're in the bathroom and want to read about what you're missing].
That being said, there's nothing I can do to prevent, how to put this, less than considerate people from abusing the app.