It won’t be the 13th. It could be the 20th.
We know the end date for Season 21 is Sunday, November 8th. We know that non-emergency patches to live are done on Tuesdays. That means the earliest Patch 2.6.10 can be applied to live is Tuesday, November 10th. Now we bring in this information…
…which they’ve stuck to since Nev made the announcement. That means the new season wouldn’t go live until after Tuesday, November 17th (which is a day they could apply a patch if something’s gone wrong on live with 2.6.10). Seasons always start on a Friday, which means the first Friday that’s more than a week after the first Tuesday they could patch to live is Friday, November 20th.