I'd say last week of November.

From a festive point of view, I enjoy seeing them immediately after Thanksgiving (if in USA), only because Thanksgiving tends to be overshadowed.

If we are speaking liturgically, then when Advent starts. Even then it would be more appropriate to decorate for Advent first and then Christmas when Christmas starts (but this only makes sense if people celebrate Christmastide, meaning all 12 days of Christmas, which, sadly, almost nobody does anymore.)

Around 312 days ago

At any point before December, is the wrong answer.

After thanksgiving

15 November. First day of the Nativity fast in the Eastern Orthodox Church. 40 days before Christmas

Saturday after Thanksgiving