I notice many of the museums have night hours. Can anyone tell me if they are less crowded at night or is it better to go when the first open with a museum pass?
Paris museums are always crowded :) I personally find the nighttime ambiance more comforting. If you have a museum pass, visit whenever your daily schedule allows it.
My personal experience from going to the Louvre twice in the late day/ evening in summer, is that it was alot quieter then the day visits. It is not however deserted( wouldn't that be a treat) ,, but quieter then daytime.
If you arrive at the Louvre on Wednesday evenings (check locally, it may be Thursday since I am now having second thoughts!) at 5:45 PM, buy your tickets and go to your favorite things to see, it is far less crowded than during the day. The museum opens at 6PM and it is much better to be at the front of the line. As you know, it is much too huge to see it all...choose what you want to see before you go...enjoy!