Some groups work 12 hour shifts, 7 days on, 7 days off. A friend of mine works the following schedule:
7a-7p x 7 days, 7 days off, 7a-7p x 7 days, 7 days off
7p-7a x 7 days, 7 days off, 7p-7a x 7 days, 7 days off
He gets 2 weeks of vacation (3 weeks starting next year), which means when he takes a week off, he gets 3 weeks off at a time.