[cobred]

If you sand a metallic base coat you have to recoat it with more base coat before clearing or you will have stripes in the metallic. (not the kind you want). You should talk to the paint supplier because all the paints have a window of working time when you can and cant apply more paint.
In other words, normally after you spray the base you let it dry an hour or 2 but no more then 24 hours before you clear it. After 24 hours you have to sand it and apply more base, let itdry, then clear it. This is to have the correct chemical bond between the base and clear.
Instructions vary from different paint brands so that is why I would check. I would hate for you to make a mistake that would be hard and costly to fix.