Filler Question

As others have said the temperature and amount of hardener will both effect cure time. Its just going to take some experimenting and practice.

I have done some fiberglass boat work. When you are laying up big sheets of fiber glass, hardening too soon can ruin your day. It uses the same basic polyester resin and hardener as bondo. One trick I learned was to chill the resin/bondo before you use it, it slows the cure.

Obviously if you have read the warnings on the can this stuff is poisonous, and stinky don't put it with your food; or seal it up somehow.
My wife would have killed me if I even brought it in the house anyway :soapbox:

A small cooler with ice packs works pretty good, probably way over kill for a small batch of bondo.