Who is they? There are some variations on hours - at a minimum, very busy days have extended hours, but if you are looking at one week that doesn't have a holiday or anything unusual during the week, it is very possible that all days will be close in crowd levels.
If you want an idea of light vs. heavy, the cost of the express pass is a good indicator. Just navigate Universal's site like you are going to buy an EP, and when you pick the day, you will see the price. If you look at November, for instance, you will see prices for the 2 park EP ranging from $84.99-129.99. In theory, that $84.99 day (Wednesday of that week) is going to be the least crowded per Universal's projections.
Also, if you Google universal crowd calendar, you will get several sites - I can't recommend one over another.
You'll have a great time no matter the crowds. November typically has pretty light crowds until Thanksgiving week with a few moderate days thrown in around Veteran's day.