Monday 4-8pm

Maybe best to stay at the airport; assuming it's not a holiday, traffic will be a bear.

You'd have to take a taxi to any of the three "sites" I mentioned. Saphan Mai is pretty much open 7/24/365. It is a traditional Thai market, i.e. "wet" (protein in all its un-refrigerated gory), but there are some eateries, and the usual stuff; anything/everything.