I used to rattle can paint outdoors until recently. A cooler day is OK if your paints and parts are warm (Pre-warm them). Them bring them back inside right away. Do your best to avoid humidity above 50%. My experience with some paints is, I would be done with a nice glossy finish, to come back later and find it dulled out thanks to the humidity. The good thing about painting outdoors is the lighting and vapor dispersion, The bad thing about painting outdoors is the bugs and dust.