I work 24-hour security. This was an experiment we did at my job that ended in disaster.

The boss moved us to 12-hour 40-hour weeks. Many of us liked having more time off (especially those of us who worked nights), but many of us hated it. And their bellyaching grew loud enough to get the boss to move us to an option between 8-hour days and 12-hour days.

The majority of the staff opted for 8-hour days, and the few 12-hour holdouts were forcing their relief to work the other 12-hours because the boss wasn't going to play that game of scheduling Tetris.

In the end, the last holdout relented and after a long period of stabilization, we're all content with our 8-hour days.