I always start eating the popcorn as soon as I sit in my theater seat, and don’t remember the last time I finished the entire bag of popcorn. Once the movie starts, I’m usually more focused on the movie and more concerned with not making too much noise that my grazing on the snacks is cut down by half. If you want to eat popcorn early, eat popcorn early. If you want to wait for the movie, wait for the movie. But there’s no magic ratio shared by all theaters, it’s just whatever pacing you happen to eat at.