If the skin of the squash cannot be pierced with your fingernail, then it's a good sign it can be harvest and if it is a deep tan. Also, the skin should be dull looking and not shiny. You don't give your zone, which would help. Usually this squash would be ready around September to October. Be sure to leave at least 2" of stem when you cut it to prevent disease from entering; it will last longer in storage.