I work a "continental" shift pattern - 4 days on, 4 days off, 4 nights on, 4 off ad nauseum....
This pattern means that two Fridays and Saturdays out of every month I am working. They are 12 hour shifts which leaves little room at the end of a shift for a rehearsal or a gig, so these are usually pushed back to when I'm not at work. I'm in two bands, neither of which are particularly busy - one is an originals band, the other is a jazz 6 piece. I blessed that everyone in both of these bands is willing to work around me and my ball ache of a shift pattern.