If the paint rubs off when you try to sand it, it's obviously not dry. Or if it clogs up the paper and won't rinse off, that's another clue it's not dry yet.

Drying time has been a major pain for me so far, so either I'm doing something wrong, or the Rustoleum paint they sell in CA uses a different formula that takes much longer to dry.

I thought this was gonna be a 3-4 day project, but it's been about a month, and 100+ hours, and I'm still not done yet. So try to be patient.