As far as I know, bondo doesn't need to cure over several days. Look at the production body shops, I do not think they wait several days and that bondo changes shape over those days.

Plus I think it's not curing, it's hardening chemically. After a couple of hours that's as hard as it gets and as long as you use a block or a board to sand with, you should get pleasant results and not see any surprises once you start putting paint on it. I have used the cheap bondo and have not had this problem, and a guy who works at a body shop came over to help me fix a dent on a fender, and he had the whole thing done and primed (with one coat of bondo, and one skim coat) in about an hour. I've done other small dents only a couple of hours before painting, like when I found things I hadn't seen before painting. No issues as long as the bondo is mixed right.

For the final pass of bondo once you have the shape right, mix bondo with fiberglass resin, then the bondo hardener. This will fill in scratches and will not have any pinholes. But it takes a bit longer to dry.