In what circumstances do departments permit graduate students to complete their program off campus? I believe that the law could make better use of formal logic. I've been accepted into a good law school. After I graduate, I'd like to use part of my career to explore ways lawyers and the law could practicably use logic. 

On a number of warrants, I believe that completing a graduate degree in logic (either a master of mathematics, or a master of philosophy) would help me accomplish that. That said, the university that operates the law school I plan to attend doesn't offer many logic courses. I have a school in mind whose math and philosophy departments teach a great deal of logic. 

However, my circumstances are such that I'd need to complete my studies in logic while studying law. Preferably, I'd study logic during the summer terms and law during the other two terms. Although, many instructors don't work full-time during the summer, which could make that plan less feasible. Alternatively, I've considered completing the course work, or pre-studying, during the summer months, then rendering the course work and completing the exams during the regular terms. 

In sum: I plan to study law away from the school where I'd like to study logic, so I could go to the school where I'll study logic during the summer terms, and only occasionally during the fall and winter terms. Thinking in or out of the box, what could I do to make this work?

Thank you.
This is really something that will differ depending on where you are, what field, and even who your advisor is.

For example, at my previous institution, the rule was that you couldn't work on your dissertation remotely until after your proposal date (meaning you are fairly far into your program - proposals at that institution were 2-3 years in for many) and only with your committee's approval. Some chairs could, and did, refuse.

Others were extremely laid back, and probably wouldn't have objected to skirting that rule.