I play AD&D 2e at lunch sometimes, and my main advice is:
Stay in character. If a player is talking about the football results, you've lost about 5% of your playing time from him starting talking to you shutting him up and the game continuing.
Don't use minis or a battlemap. Setting this up again uses up a lot of time, and preparing for a battle is also very time-consuming.
Play quick and easy. Don't have many encounters planned that will drain the party utterly. If the battle lasts longer than the rest of the session, by next time everyone will have forgotten what's going on, whose turn it is, etc.
Make either a linear quest or completely open sandbox. If the players want a story, make it fairly linear. You don't have the luxury of time to waste wandering off in the wrong direction. If they want a bit of freedom, set up a (mega-)dungeon with regular exits so they can leave quickly, and let them wander around a little hitting things.
This is what I use, and I've been fairly successful. I'm sure there are other options and many other tips, but this is what I've tested personally