I am assuming that you want to head to what is called the south side of the mountain for your hike. Unless you are going for that hike on a week-day, you will lose too much time to get to Tremblant on a Saturday or Sunday morning because Mom and Pop are bringing the family for a pic-nic, a day out or mountain biking and traffic is a pain ( it may take you more than the estimated 1.5 hr to get there). Tremblant is crowded in September and October not only with the "locals" but tourists because the leaves start to change colour earlier up north and parking sometimes is difficult to find.

By mentioning the other side, I was referring to the North side- I have been told that there are good hiking trails (even skiing is less crowded in the winter) but have never been there myself.