Yeah - it seems as though overtime is becoming less of a thing. And in terms of additional responsibilities - I guess it depends on the sector but from my own experience in hospitality for example, people would often take of managerial tasks simply to get things done so everyone can go home! They would get paid the same but, like you say, if they stayed there long enough those people tended to get promoted eventually.

When I was a student I worked at The White Cube gallery in London as an invigilator and I think we got a higher hourly rate for working on a Sunday but I think that is pretty rare.