Not to say my experience is "typical" or even "reasonable," but I was the resident PSM at a non-Eq dinner theatre for 2 seasons. During that time I had no guaranteed day off, and no "set" hours as I was a salaried, exempt employee. If I didn't have shows, rehearsals, or meetings I could choose to take a day off whenever I wanted (and set my own work hours outside of rehearsals and performances), but I was required to work a minimum of 40 hours per week.
Sometimes depending on staffing, I was in rehearsals for one show and performances for another which meant I worked all 7 days for 4-6 weeks at a time. This happened on 3 occasions and by the third time, I asked to be compensated more per week since I was working 2 shows.
Towards the end of my time there I started working only 32 hours a week and convinced them to give me the other 8 (and not dock my salary, which is illegal anyway) due to the vast number of weeks I was working 50-75 hours a week.
In exchange for our exempt status, the 5 salaries employees received 2 weeks of paid vacation. However, I was not usually able to take it except in the rare times I had another SM on staff who was running a show.
Once, I worked 40 hours between after midnight on a Sunday (12AM monday) and after a matinee for a show I was supervising on Wednesday, then took Thursday through then Tuesday off, then worked 40 hours between Wednesday and the next Sunday, thereby taking a 7 day vacation without using vacation time.
By the time I left, they declined to pay out my vacation time (that I never used in 3 calendar years). This was technically fine because there was zero written policies and not even a written offer that cited my vacation time.
SO, get your working conditions in writing! If not a specified day off, have a superior sign off on a schedule you propose so you can at least prove you were asked to work a certain number of days/hours per week.