Perhaps obvious to everyone else, but I've hit upon a little trick for better coordinating game time. Instead of announcing "Game will be at 1 o'clock" I've been doing something like "Doors open at Noon, Game starts at 1." This way, the people that want to hang out, level their characters, decide what they like on their pizza, etc all show up at noon, and the people that are running late or decide to come at 1 arrive with the expectation that they're going to walk in the door and immediately start playing. It also provides a natural transition point from the arriving/hanging out mode to game time, which otherwise makes me feel kind of uncomfortably teacher-y, calling the whole class together and whatnot. Try it out, maybe it will help you too.