If I wanted to be sure to stay in WDW for certain dates, I book rack rate at a resort that I am comfortable with staying in even if there no discounts become available. When/If discounts do become available, I will call or go online and try to change my reservation, to a better resort or price. Personally, I prefer to book as soon as possible. This year, with SW:GE opening in the fall, I would be even more inclined to book early. If you want to rent DVC, you need to book 11 months in advance for best availability. (or as close to that as you can)
For example:
We booked our late Nov - early Dec, 2019 trip in Dec 2018.