They sold it to me as "flexible".
Well, "flexible" is most often not in favor of the employee. I'm not exactly flexible though. After exactly 5 weeks the schedule just repeats. I know how I work tomorrow, next week, month, year or decade. So it's very predictable. There's really only 1 rough transition during those 5 weeks, the rest doesn't require sudden changes in sleep pattern.
What I meant about not keeping a regular schedule is that I can't do something at a specific time on a specific weekday every single week, because at least once every 5th week I'll work at that time.
Had it been unpredictable or as they so nicely try to sell it "flexible", then I would have quit a long time ago.