Can you work in a garage?

The dilemma you are facing is blush. With epoxy there's a period where you can apply fill coats and you will get a chemical bond. If you wait too long, blush can form and then you should scrub the surface and or sand too? Obviously, you want to avoid that. Depending on the brand you are using and wether it's blush free or not is the determining factor. I would get on the phone and talk to the Co. who's epoxy you are using and see what they suggest. I try to plan my glassing so I am doing fill coats every day but I do work in a heated basement.