It looks to be indica dom so probably relatively short flowering time, 8-9wks.
It's beautiful, btw.
It could be done as early as late September, maybe a bit earlier. If that's only a few weeks longer than you have until frost then maybe you should induce flowering early. Like you said though, it'll be huge by then. If you had it in a pot and had the roots restricted you could keep it small but training is the best you could do in your situation.
I don't know man, make a conservative guess on when the first frost will be, and ten weeks before that start to cover it somehow to restrict light...if you do it for two weeks you can stop and it will keep going. But covering it would be the hard part and I don't really know how that would work in your situation.