My guess is that they are aiming for November due to when pre patch is dropping. So I am going with the 17th. I would say the 10th since that would be a 4 week pre patch, but that would mean season/raid drop would be the week of Thanksgiving in the US.
So i am going with 5 weeks of pre patch and then new raid opens up just after the Thanksgiving holiday.
I do not think it will be any later than Dec 8.