Believe it or not, it's not too early to start a mock scrape now. In fact, if you have the chance, I'd say to do it earlier than October.
Be sure to choose your spot carefully. Most people put them under a branch that's too high for the deer to reach. Remember that a deer, even a mature buck, isn't very tall. Wear rubber boots and gloves when you set it up and when you go back to check it.