We recommend that in warmer conditions, it's best to use a slower hardener. Mix smaller batches that can be used up quickly, or pour the epoxy mixture into a container with greater surface area (a roller pan, for example), thereby allowing exothermic heat to dissipate and extending open time. The sooner the mixture is transferred or applied (after thorough mixing), the more working time will be available for coating, bonding, lay-up or assembly.
In cold conditions use a faster hardener, or use supplemental heat to raise the epoxy temperature above the hardener's minimum recommended application temperature. At room temperature, additional heat is useful when a quicker cure is a desired.