I was paying close attention last year because I knew I was going this year and I'm almost certain that the hours didn't change until about 3 weeks before. So I would look to the beginning of November for the changes. I even remember the threads on the dis about the ticked off people who got screwed out of their pre-opening park ADR's because the hours extended both in opening and closing.
I am going ahead and planning based on last years hours and will adjust as needed about a week before.