From the information that I have gained over the years, IMO the general rule of thumb for applying a 2nd coat of epoxy over the 1st is to do it within 24 hours of applying the 1st coat. Otherwise a light sanding with very fine waterpaper is necessary to obtain a long lasting adhesion of the 2nd coat. Old rod finishes should also be sanded prior to a touch up or you run the risk of poor adhesion and pealing over time.