Hello, I work and live at a University. My school provides me with an apartment on campus and my salary REALLY reflects that.

Anyway, there are instances that I am required to be on-call. Sometimes I am on-call for 24 hours and there are many times in which I am only allotted to leave campus inside a 6 hour window. This can happen once or twice a week. Currently, we are only allowed to mark time we "work" on our time sheets (responding to calls, interacting with students, etc) but there is no place for us to indicate the many hours I am required to be on campus because I am on-call. Even if I am on call, I am only permitted to stay inside of my own building. I not supposed to even take a walk on campus. It does not feel completely right to me that I am not marking down any of this time. Thoughts?

I think there is an issue here. By federal law any time you are under your employer's control for the benefit of your employer (i.e. being on-call with restricted activities), your employer is obligated to pay you. I am assuming here that you are paid hourly (hence the time sheet) and not salaried - is that correct? Here's some reference info:
Paying Employees Who Are On Call or Traveling for Business | Nolo.com