As far as I know there isn't a built-in method to have a time frame for restricted software, it's either on or off. I would suggest creating a feature request. There may be some other really unpleasant ways to make this happen though with policy.

Thank you. I will put in a feature request and keep looking at other options.

You could technically script this... but there are so many pitfalls I would stay as far away form the idea as possible. With that said, you could pay JAMF to write something up, but I'm not sure the cost/benefit would work out. That's assuming that they're not interested in developing this functionality as part of a feature request. Apple has built in processes for handling certain time based restrictions, but as you know they are not granular enough to accomodate what you're asking.

Working in education myself we've always had a certain saying... "Sometimes, there's no technological fix for a social issue." I'm not familiar with your particular situation so I don't want to speak like I do. If one of our students were to be distracted enough by a school supported application, but we would have our faculty try and work them trough the issue. If that wasn't enough we would simply assign the students work hours or some other form of punishment until they learned to deal with their time appropriately. If they don't after that, welll...

How about creating a policy to search for process itunes.app and kill it during the hours of 8:00AM and 1PM with a checkin of 5 minutes. That way each time that they load the app between 8 and 1 it will close shortly after. They will get frustrated and eventually realize that it isnt worth pursuing. This can be modified at will and even restricted to user/computer groups if needed. Hope this helps!