If I remember correctly you are using the same thing I'm using. Uscomposites 635/556. If I am correct this is a very sloooooow epoxy. I have used it down in the fifties with no heat, but it took more than one day to harden. I can't remember for sure but it seems like I've had a boat tacky three days later because of the temperature. I've never had any trouble from this...it's just simply too long. After those experiences I bought a small electric heater to heat the boat. I've also used light bulbs placed strategically around and inside the hull. I try to keep the heat up enough so the boat is ready to work on the next day. 70 degrees easily does this.