It will be bidding on bags of fish at this one. I believe a "buy it now" table will be a feature for the fall MCA auction but not this one. It is currently a feature at some other auctions (e.g. MCAS, possibly GDAS, can't remember for sure).
Usually lasts until around 4PM, based on what I've been told of past auctions. Again, this can be unpredictable, as the last MCAS auction I went to normally would go to 5pm and instead went to almost 8PM.
But if there's something you really want, pay the $2 priority bid fee and get the item bumped to the front of the line. Doesn't guarantee you'll win it but at least you won't be gone all day just waiting for one bag and possibly miss it.