The time between base coats depends on the reducer he is using and the current temp. Refer to the paint "P" sheet for guidelines. You can wait as much as 24 hours between DBC base coats before you must scuff the surface before re coating. The main thing to remember is give the base plenty of time to "off gas" the reducer. Three coats is considered minimum to get good coverage and is the norm. Three to four good coats of clear is also the norm. you cannot do any spot sanding on on the final coat of base before applying the clear especially if you are using metallics.