From the Klass Kote site: For optimum results, apply to substrates, and store the product between 50-80° F. Humidity can slow the curing processes, but in most cases, Klass Kote Epoxy Paints are very forgiving. For best results, use product below 70% humidity.
I have sprayed in the rain standing in my shop door under the overhang of our back deck. I would not normally do something like that but I started a project and was determined to finish, no problems that time.