The movement of teal depends alot on the weather. Any north wind can push them out overnight, or alternately, push them in. If they have a good foood source and a reason to stay, and the weather stays mild with no fronts, they will stay for atleast some time in a given area. Gw teal can come in in september and stay till february. I have seen bw teal into november, but most are usually gone by October.
"If you have to be crazy to be a duck hunter, i dont wish to be sane" Robert Ruark
Its always duck season, there is just a long break from february to september.