The roadmap begins with Beyond Light's release on November 10, and it currently covers everything through January 5, 2021. However, the Season of the Hunt will continue through January, and Bungie says there's more to come after January 5.
Central activities will roll out throughout the season. On November 10, new quests called Empire Hunts will become available and the new Europa strike, Glassway, will open. November 17 will kick off the proper seasonal events with a (likely weekly) seasonal mission and Wrathborn Hunts, which seem to be tied to the newly revealed Hive Cryptolyths. Finally, the new raid, the Deep Stone Crypt, opens on November 21.
Two regular events are also confirmed on the roadmap: the first Iron Banner of Season 12 coming on December 8, and the annual Dawning Christmas celebration starting on December 15 and continuing through January 5.
The roadmap footnotes are less informative overall, but they do contain new details on upcoming Exotics. For starters, we now know that the Salvations' Grip Exotic grenade launcher will have its own Exotic quest which will be available starting November 10. Fans have speculated that this weapon will drop from the Deep Stone Crypt raid, and while this is still plausible, the timing of this quest suggests otherwise. Just as importantly, the Exotic list mentions a new weapon: Duality. Based on previous datamines, this is believed to be an Exotic shotgun, but the nature of Duality remains unconfirmed.
Here's an important date not listed on the roadmap: Destiny 2 will come to PS5 and Xbox Series X in early December.