I read something here about duct taping a peice of plastic to the floor overnight to see if any condesation showed up. If it did, you need to wait longer. If it was dry you were good to go.
Of course I've never done epoxy before...
The "tape down plastic test" is to see if your floor has hydrostatic pressure; that is moisture being wicked or forced up from the ground underneath the slab. Excessive hydrostatic pressure can cause coating to separate from the concrete - not a good thing.
Different coatings have more or less tolerance for that moisture, so if you do run the plastic test (use a 3' b 3' piece of plastic) you'll want to check with your supplier about what to do.
If it's a lot of pressure there are solutions, some very good ones, but they can be pricey.
As far as the original question of when you can coat after rinsing a floor - again, depends of the coating (seeing a pattern here?). For example, many epoxies require a bone dry surface, whereas our Bondtite 1101 can be applied while the floor is still damp, that doesn't mean "moist," and there can't be any standing water, but if yo see areas where the concrete has become light, you're probably good to coat.
