Read the mfgr's instructions. But I'd wait at least 2 days between layers - especially after the 1st coat. I've found that sometimes the new coating can partially dissolve the coat it's being applied over which can result in wrinkled paint in spots when the new layer dries. At least something like that happened to me. O - and if I understand correctly, paint doesn't 'dry'; it oxidizes or 'cures'. So when you paint over a layer that isn't fully cured you're depriving the under coating of its source of oxygen - this'll delay the curing process considerably & just make thinks worse.