Late Fall = early December.
The first day of Winter is December 21 (as someone said above). It's possible SWL will be open by Thanksgiving, but I would not make a special trip on the basis that it will be open.
As a counterpoint to myself, Disney advertised "Summer 2017" for Pandora. Technically Summer 2017 started on June 21, 2017. But Pandora opened May 27. Then again, they also said "Summer 2018" for Toy Story Land and that is opening June 30...
So the bottom line... who knows?