I don’t know where you’re located but I glassed a board in Southern California about a month ago when we were experiencing a major heat wave (at one point a city in the Valley reached 119 degrees F- I told my wife, “If it reaches 120 we’re going there, just to say we know what 120 degrees is like.” Unfortunately (?) the following day went down to like 112.)
Anyways, I was working in a garage that had to be over 90 degrees. I never had problems using RR epoxy with slow hardener. 40 minutes plus working time.