Piece of advice, from having participated in a lot of these: you will often get many more volunteers with a more-focused timeframe. That is, if you say "these four hours are going to be the Main Push", I'll look at that as time to block out, and make a particular effort to get there, whereas a squishy "all weekend" often leads to never quite finding a slot.

That's not exclusive with the all-weekend -- you can stay open the rest of the time -- but telling folks when the heart of the party is tends to motivate more of them to make it, and get a larger army together...