Depending how smoothly it goes, if we start at 1pm, I would say you could be done by 3:30 maybe 4 if all goes smoothly. Sometimes it takes a bit longer, less if you don't care about the raffle. We'll be doing a lot of the raffling during the swap, and having the raffle ticket numbers on a board so people can check throughout the swap so you don't need to wait until the very end or anything for that.
If you wanted a "Safe" time frame, say it'll be over by 5pm, most of us who'll be cleaning up and stuff will be there until then at the very least.