Ideally you want to glass indoors in 70 degree temps but that doesn't mean it can't be done successfully outdoors.
Epoxy moves better in hotter temps so I recommend heating the resin first so it flows nicely on the board while hotcoating.
But, it's best to have the surfboard and resin at the same temperature so the resin doesn't get "shocked" when hitting a colder board and getting a little funky. So if you can keep the board and resin in a warm room and bring them out at the same time you'll have better results.
Also beware of wind pushing debris onto the board while outside, it's almost guaranteed to happen :)
I've glassed boards outside plenty of times in the summer months and they turned out fine..
Overall don't expect perfection when you're working in a non-perfect environment. The end product will be a ton of fun to surf no matter how it turns out.