Painting steps from primer to clear

How long do I need to wait between each step of painting? That's a thing I feel I've never been entirely clear on. I believe I've read that after a certain stage in the process it's actually important to not wait too long or you have to sand the earlier layer to get adhesion.

I've used epoxy primer on a fender I've repaired and it's been waiting a few days, I've sanded it with P320 grit. Since this was an epoxy sealing layer I realize I should wait longer for best results and sanding was gonna be required.

Next step is to lay down a high build primer. I believe if I let it wait until next day or even longer then I will have to sand before base coat. I should put the base down inside a few hours max? And the same is true for going from base to clear, it should all be done inside a few hours unless I want to start sanding?