I've sprayed nitro in those conditions from a gun, and it's been OK, but then a gun is adjustable, whereas a can isn't (and you're already at the mercy of the pant/thinner mix in each can, which can be quite variable). But that's mainly because I really wanted to get a move-on and finish bits and pieces. Last summer here in the UK it got well over 30°C, and that was just too hot to spray. But I do prefer to spray at lower temperatures and on still days.