Probably 70+ degrees. But depending on the nature of the project there are things you can do to get the heat up. Space heaters under boat covers are one example.
Really just mix a pot of quick west systems in 40 degree heat it will cure in 15 mins. with that in mind , how can you say such thing's ,Boomyal or kloss not a challenge im really just wondering?
Epoxy tends to generate it's own heat..... 70+ is the optimum temp. Make sure it starts out that way by keeping it in a 70 degree area before and during the mix.
Covering the area with a bit of heat will help. ..... just don't have a flash fire!