--Here is my problem with this whole thought, or at least how it all sounds when I read it. There are no expected hours, just a limit on the amount you can use. This whole idea sounds extremely like, "We want to be as good as X band, but we don't want to practice as much as they do. So, why don't we try to keep them from practicing so much so they can't be as good."
Bottom line, if you want to use the whole 8 hours, then use it. If you don't, then don't. Its not a secret, and acquiring a job you should know what the expectations are when you get there. If you don't like it, find a job that doesn't have it. I guess I am just tired of the fact that society is leaving the work hard to get what you want mentality and speeding to regulate others so that it can be more "fair."
Good luck to you and your students!