If I'm kept busy I'm happy to work any day. What bugs me is when I'm called into work on what is suppose to be my day off when there is little to no work to be done. I end up inventing jobs to do while wondering why I was called in, in the first place.
12 hours is a long day, always it easier when there's no one lurking over your shoulder. I do my best work when I'm left to my own devices.
I used to work a minimum of 10 hours when I was a teenager sometimes more than 10 days without a day off. It was far from legal but I was thankful to have the income, it made sure I could pay my rent through college.