No plans to go to this one, I'd probably end up buying something and I've no room for the cabs I already have.

How long the auction depends entirely on when they start, and how much stuff is there, and whether they have more than one barker working at a time. First W-S auction I went to started around 10:00 am and finished about 9:30 that night. The next had more stuff there, started later, yet finished two hours earlier as they ran two barkers and worked both sides of a row at the same time.
One suggestion I'll make. Take a cooler full of your favorite beverage, snacks, sandwiches, and some reading materials. If you're after MAMEable cabs, those tend to be sold pretty late and you'll be there all day. The food there is marginal and overpriced, and there's going to be at least a few hours of the auction where they're selling stuff you have no interest in. Use those times to go outside and take a break. Oh, and wear comfortable shoes. 8+ hours of standing on concrete is hard on your feet.