You'll get different opinions on this but, I wait until its just "skim dry" and recoat. Most wait until it stringy when you put your finger on it and then recoat. The reason that I wait just a little longer is that, I want to make sure the solvents are out. I used to have a solvent pop problem when I first started. That can be a cause of several reasons but, I just want to make sure that I can build to 3 or 4 coats.
DaveK