Auction times vary wildly, I have been out the door at 3 PM before and I have been there until 10:30 at night, it really all depends on how many things get consigned at that particular auction.
Btw, one trick I learned is go the day before while all the consigners are lined up and waiting to unload and see if you spot anything you want, a lot of times the owner will just sell it to you right off the back of the truck. This works best with $100 games, decent Jamma conversions that aren't gonna bring high dollar at the auction. I have found a $100 bill will usually buy these before they even make it into the auction (seller saves the entry fee, and the commission which will cut $25 off a $100 game, $38 off a $200 game, $41 off a $300 game and so on.