If you know how to take care of meat in warm weather I wouldn't worry too much about the meat spoiling on a elk shot in September. The big thing with a elk is to get the hide off of the meat and if you are packing it out then bone it and get it into a bag to protect it from the flies and bees that will show up. The last bull that I shot in September gave me 360 pounds of boned out meat and I didn't loose anything to spoilage and the weather that day it was hot.
A big aide for a novice elk hunter is the Colorado Elk hunting University that is on the divisions web site. I haven't gone through it to see just what it has in it but I have heard others say that it is worthwhile.