I think that it has to do with a second primer coat. I'd wait but then I am a perfectionist and would of sand blasted the thing down first. Id do something like:

get to bare metal, wipe it with a solvent, dry, spray a very light coat of primer, wait 20, spray another light coat of primer. wait 2 days, sand with wet/dry 600grit, spray another light primer, wait 2 days and sand again with the 600, wash with joy soap and dry then spray a few light coats of finnish color.

If it is just gonna be flat black, and you are happy that you sprayed it all with enough primer, and your dying to piant in 24 hours, see if you can heat it a bit with a blow torch from a good distance to make sure that the primer has hardend then sand and spray the finnish coats. Do not heat it more than warm to the touch, then wash it off with joy to get rid of the minute amounts of oil from your hand.

Dont use anything with a lower number than "600" for the wet dry sand papaer. You soak the sand paper in water to sand it smooth. You can get that at an auto store.