it can last longer than that usually if you are smart about the way you set it up. We had many 80-90 degree night sessions(I live in atlanta and I wouldnt recommend hitting a rail in 80+ degree temps. It sucks hardcore). But we got snow last may/june to last until the next day in the summer. We even built a jump with the extra snow one night on another session. It was prob only about 3-4 trash can loads too. If you put the turf down, and put a little bit of snow on top of it, like an inch or so, you use less snow, but you get the same effect as deeper snow(unless you have to build a jump with snow).
You can also use bags of ice on top of turf. It actually works surprisingly well, and you dont need much at all.