69 Cuda resto

You want to let the primer to sit a couple of days for the solvent to flash off, then sand the primer.

Do not sand the base coat, you will cause the metallic to streak, base should go on flat, do not try to make it shine when you shoot it.

As for sanding/polishing the clear coat, time will be based on the paint system you use, and the temperature / humidity when the paint is shot and the number of coats of clear you put on it, I suggest a test panel sprayed at the same time as the car to test this if you are unsure.