If you want to trade players, you can do it anytime. But any big move involving non-skating individuals (especially if it includes Bergevin) depends on the schedule. The first window was the 3 days off following the 6-2 loss against the Ducks in October. But in November, the Habs have a gruesome schedule that would not allow this type of change.
I'm circling December 9th on the calendar. That day, the Habs face Edmonton and then are off for four days. That could be the perfect time for a major shakeup. Following that break, Montreal welcomes the Devils on the 14th. But after that ? Montreal has 8 games on the road and doesn't come home until January the 2nd. Plenty of time to make major player moves, maybe sell players to tank and be away from the boos at the Bell Center.
If nothing happens between the 9th and 14th of December with Bergevin, Timmins, Muller, Lefevbre, etc... then nothing will happen until the season is over, IMO.