Scuffing Epoxy Primer

I too am not a paint pro but I think the time limit has to do with binders - once it sets up over 24 or 48 hours it get surface hard and won't bond to your top coat . I use a epoxy primer last time also and once done with the priming it was a week later b4 I could shoot paint on it.But that was ok cuz I wet sanded the whole car (with 600) before I painted it and got the best finish yet . with no lifting or bubbles