So I've ordered the caliper painting kit from TireRack. In reading the instructions on their website, I see that I have to wait 2 hours after painting before reinstalling the wheels and 24 hours before driving. I get the 24 hours part, but why can't I just put the wheel back on after painting?

Where does the wheel make contact with the caliper that I would have to worry about waiting 2 hours for it to dry?

Well you can put it on.. be careful.. you get that goop on the wheel & its on there for good. when I did mine, I just did one side of car at a time, very careful bolting wheels back on & you shoudl be fine. cure time is the key! :)