I always try to book our reservation as soon as the Disney web site allows. I was able to book our September 2016 trip in August 2015 and our December 2018 trip in August 2017. The Disney web site apparently allows reservations for the next calendar year to begin about August of the previous calendar year.
Our next trip is September 2020 so I expect to be able to make the package reservation in August.
This is only the regular rack rate package prices for 2020. As I said unless you are looking for specifically a really rare room type such as a luxury suite type of set up, I would sleep in and check it that morning. Marie