Kathryn Hahn wasn't setting up a bait last week when she said filming would be sometime next moth as she got it close to the new information on when the production starts for Agatha: Coven of Chaos which would be in Atlanta on December 5.
Considering that October is about to end, Kathryn Hahn's update on the filming of Agatha: Coven of Chaos is relatively close to the official start date of the production of the spin-off series according to Production List as it will begin on December 5 in Atlanta.
In the same listing, it contains the summary of Agatha: Coven of Chaos, which introduces Agatha Harkness as a powerful witch who has lived for centuries, thus, being one of the top, and she is the governess of Franklin Richards, and tutor of Wanda Maximoff.
This summary teases the connection of Agatha Harkness to Franklin Richards, son of Reed Richards in Fantastic Four and it is fitting that Agatha gets her own show to establish her origins better and her role in the MCU once the son of the First Family arrives.
As per the summary, it draws some kind of line between the past of Agatha and her future in the MCU. It is yet to be determined what the spin-off would be about, whether it will be the past or the events after WandaVision, it could be both, too.
When it was first confirmed that she will have her own spin-off, it was titled as Agatha: House of Harkness but it later changed into Agatha: Coven of Chaos which hints that the show might not be just around Agatha.
Agatha: Coven of Chaos sits right in the middle of the Phase Five of the MCU, that's the only thing definite for now aside from Kathryn Hahn reprising her role but rumors are already circulating who will be with her in the spin-off.
Agatha: Coven of Chaos does not have a definite release date yet, just a release window on Winter 2023.