I'm in the Mojave Desert-- You can fly in any temperature that "you" can stand (tolerate), however, don't leave your hot glued planes in hot cars, garages or trailers--that is where you will lose the integrity of the glue joints!! Constant, still exposure to very hot and very cold temps weaken or break the glue joint!!!
I fly all the time in temps above 100 out here and have never lost a hot glue joint!! Of course, do a good preflight on your airplane before you launch!!