There’s a chain of theaters (primarily) in the LA area called Arclight Cinemas. One thing they’ve been doing since their inception is having exactly three movie previews before each main feature. No ads, nothing else. Just those three previews. I haven’t timed it, but that can’t be more than seven or eight minutes off of the scheduled start time. The chain gets a LOT of things right in how they approach the theater experience differently, and that’s definitely on the list.