While I applaud your tremendous effort, I can't help but sympathise with your plight, Alan. For you see, the Happy Hopper never even has to miss the first 20 minutes.
It's all in the planning you see. You don't hop blind, but you print out the schedule for you designated cinema. Next, crease the page along its horizontal & vertical axes, and fold and slip it into you pocket. At the opportune moment, this surreptitious sheet will show you the way...