You are an old hand at epoxy, so let's assume you metered and mixed it properly. Then the only variable left is temperature. Gel time specifications are for a specified amount (usually 200 grams) and ambient temperature (usually 77 F.), in a cup. Whatever that gel time is, at 18 F. higher ambient temp it will take half as long, or 18 F. lower will take twice as long. The curve is nonlinear, but you get the idea. Furthermore, the curing epoxy generates its own heat, and that accelerates the reaction, which produces more heat, until it completes its cycle and hardens completely. If you take the same 200 gram mass and spread it out on the boat, now it has more surface area to give that heat off to the wood and the air, so the gel time is retarded even further.

If you were to take a 200 gram cup of freshly mixed epoxy and stick it in the freezer, the reaction would stop. You could take it out 6 months later, warm it up, and it would continue to cure as if nothing unusual had happened. The same principle applies to the boat. It doesn't require an oven, but a little extra heat would speed up the cure quite a bit. Even a 100 watt light bulb hung below the hull would dramatically increase the cure rate.

If that doesn't work, we're back to metering and mixing, and that could be a messy dilemma. I'll cross my fingers for you.