As epoxy cures it is an exothermic reaction (produces heat). The cool thing about epoxy is it will kick off quicker if that heat is not dissipated. This is why the epoxy in your mixing cup sets up so quick, it feeds off of its own exothermic reaction and speeds up the curing process. This process is slowed down if the heat dissipation is increased, say in a thin film or with a substrate added to dissipate the heat. Both of these I just mentioned apply to fiberglass, you have the epoxy in a thin film, and lots of glass mat to help dissipate the heat. Like said above, adding heat to your part will help speed up the curing process.
What many people don't realize is your resin needs to be at a temp of between 65-85 degrees to cure properly. Your garage may be 60 degrees when you go to start glassing, but your resin very well could be 40-50 degrees from sitting in the cold garage all night. If you are going to be doing some glassing(and you live in a cold place), preheat your resin before hand. Depending on how cold your climate is, I would put your cans inside your house for about a day before glassing. With epoxy, everything depends on temperature.
I used to work as en engineer for a company that constructed heavy machinery foundations with epoxy. We would employ steam heaters and large enclosures to warm job sites and our epoxy for approximately 48 hours before we would even attempt to mix.
Hope some of this helps, good luck.
