Rex,I would give it 3 days minimum to let the paint dry thoroughly then use 320 grit sandpaper, also don't use a lot of pressure when sanding paint you don't want the paint to overheat and really make a mess. gently warm your spray paint (and keep it warm) to reduce spitting.
Rex
Thanks - I kept that spray paint inside warm at around 75 degrees F. Three days . . . the wait will drive me crazy. I normally sand very gently . . . I've been using 400 grit tho . . . but I do have 320!
Mark