I would not sand "enamel" until it was rock-hard, totally cured. After a day or two, enamel seems cured but that's only on the surface. Enamel cures from the surface down. It will continue to cure for a month or more despite what it says on the can. It has to be cured enough that your fingernail can't leave a dent in the paint. I've been to Dupont's refinishing school years ago when they were still called Dupont. Lacquer takes a while to cure fully but so does enamel. As a rule of thumb, enamel is softer than lacquer when cured and you have to use the matching clear just to avoid possible interaction between color and clear. Lacquer is less fussy about clearcoats whereas some enamels (Painters Touch) will freak out when topcoated with good clear such as ClearMaxx 2K. That came from experience and an expensive lesson learned. Can you say "Alligator Paint?"