Generally, the earlier the better. In Disney terms, we are incredibly close to your travel dates. Dining reservations have been open for nearly 4 months already, and in just a week and a half, the 60 day FastPass+ booking window will open. If you know you are definitely going, I would start the process immediately. You already may reduced resort choices because it's so close.
Also, if you're staying on property, there is a Fall room discount going on, but the booking period ends TODAY (9/18).