Drying time depends. Curing time is also important.
For the brightside I usually give it 24 hours. When my garage was actually part of my house, I used to get up super early in the am, wetsand, roll on the paint, then take a shower and go to work. Repeat the next day. Start on a monday and for about an hour and a half extra time in the morning by friday I would have nicely painted parts. Now that I live in brooklyn and the garage with my painting supplies is in Queens I have to wait till the weekends to do it. Curing takes about a month (rustoleum takes about a month and a half) so after your final polish you can use the parts but no waxing for at least 30 days. this is pretty much true of professionally painted parts also so it is not a big deal.
For the rustolem, when I lay on that first thick coat I give it about a week and then back to the 24 hour rule for the thinned rollered paint coats. Since I usualy do about 8 coats of the rustoleum I end up going up to 1500 or 2000 grit sand paper (usually just to take the dust and junk out at the end - by the 4th coat if you have been sanding between coats the paint should be fairly orange peel free).
Rustoleum makes a clear you can use over their paints but you must scuff you top layer and then spray on a good 3-4 coats sanding in between. I know this sounds like a lot of coats but really the paint is so thin that you can see the base coat through the first three. If you have a tank with a lot of body filler in spots and you are using a color like black you may even want to do more coats than 8 (you have to play it by feel and ear - remember the more prep work you put in the better it comes out, the paint is just a covering).
The final thing I learned is that while brightside is tons easier to work with and requires less coats to produce an even shine - it prefers to be rolled over a coating or primer than bare metal. Even the old paint is preferable. Freshly blasted pieces you may want to consider laying down a primer coat. If you have a a tank with old paint and scratches you are good to go, if 50% of the bare metal is exposed then you should to primer.
With rustoleum, the stuff loves bare metal. It is a rust paint so it lives for bare metal. It doesn't really care what it is put on top of however and is really really fuel resistant.