Sabatoa we had a slightly-earlier-than-average start last year - even the podunk ski areas like Mt. Holly and Pine Knob were open Thanksgiving weekend. In a good year, these joints will open earlier than Thanksgiving and that gives the impression of a longer season.
Seems to me like the first week of December is pretty much what to expect and they target Thanksgiving optimistically, knowing it will be hit or miss. So we're a little bit late this year although Boyne was open last weekend.
Typically, the big resorts don't open until Thanksgiving either way though, because they depend so much more on overnight guests/tourism.
Keep in mind that unless we have a br00tal spring, most of the bigger places should be open through the first weekend in April.