Instructors do their tests as soon as snow arrives, usually mid December on the top. Locals and national teams ski week before Christmas and tour operators usually start Christmas week.
Usually enough snow for Christmas. You could look at the archived web photos on this board to get an idea,
I agree with the above. The ski season is "officially" opened around Mid december (whether there is snow or not). I think most people head out for Christmas. Although looking at recent years, you cannot guarentee snow at any time of the season.