It'll depend a lot on your workload, and different courses have different workloads. Although you don't need to go out all the time, it is important not to isolate yourself socially, and make some time for your social life.
I think the fact it's spread out through the week could be a bit of a problem. You'd need to make sure to avoid clashes with lectures, seminars and tutorials, which aren't always on a predictable schedule. The weekend hours should be fine. A lot of people work/volunteer one day a week at the weekend anyway.
I don't think you'll know 100% how easy it will be to fit in until you get your time table, but I would have thought 6 hours a week would be do-able for most of the year.