how long do you have to wait to wash the car after painting it with a rattle can?

Wash-wait until it is dried, can should approximate dry time.
Wax-give it a good while, this is what can screw things up. You can trap solvent in the paint that needs to evap off.

i figured i shouldn't wax for a while... the can says 24 hours, but i will give it a couple days just to be safe?

Sounds good. As long as it isn't anywhere near tacky there won't be a problem.

OK, so the "correct" duplicolor paint is not even close for a match... it'* way too light. is this normal for a car this old, or is it possibly my car was repainted (or the RPO sheet is wrong?)

I wouldn't have expected it to match. Some paint stores can scan your paint and get a reading that they can mix up for you. Try that. These are almost always an EXACT match.

This worked to the tee for my car. Didn't work so well on an 05 Sentra or a 95 Civic I've played with recently.

I had the same problem. GM varies the color by year/VIN. Go to a reputable auto body supply shop and ask them to mix a batch with the variation code that matches your vin#. When I first painted my car with duplicolor it was WAY to white. The rattlecan the shop mixed for me was very close to perfect. You really need to look hard to see the difference.

paint usually gets darker when it dries...did you let it dry?

yep. i will probably go to the local paint shop later and see what they recommend.. but it won't come in a rattle can if i get it custom made right? i think brushing on would look worse