Most Duplicolor primers are lacquer, which can be painted over with enamel. BUT! I would give 24 hours after my final primer coat for all of the lacquer solvents (usually a lot of acetone and other aromatic solvents) to go. If you keep them in an area that won't allow smells to get to where you are, your nose should recover enough to tell you if the parts are still putting off vapor. To my nose, most Duplicolor primers and base lacquers smell "fruity" - almost like apples until fully cured. You don't want these trapped under an enamel. A flow of warm (not hot) air can speed removal of the vapor from the surface, but it still needs to work its way out through the film.