Usually they will drop the rest of August, September and October all at one time. In 2019, it was at the end of April. It appears that in 2018, it might have been in mid-July (I'm looking at my old email files so I'm not 100% on this date). I believe in 2019, they dropped the premier hotel rates first and then the rest of them about a week or so later.
The next group after that is usually November through mid-December (cutting off before the Christmas week).
With all of the uncertainty in the travel world, I would be very surprised to see them release a large block of dates at one time. But I've been wrong before!