Yes, you can go inside without fee before 9am (better to be 8:45pm).
For parking, before you can park in the parking lot. But now they changed to use the machine, it is not so expensive. Or you can park in the street around there.
In summer, you need to pay after 7pm too. They have a special event for Chinese mid-August Festival. Everyone will go there at night.
Also, it is better to go in the morning, because some building didn't open at night.
Just remember, a friend of mine renewed the Access Montreal Card few months ago ~$5-7/year, can go to the Garden for free anytime, discounts for museium. Think first card may be more expensive. Call City or http://ville.montreal.qc.ca for details.