From Longman Dictionary of Contemporary Englishbe on/off dutybe on/off dutyto be working or not working at a particular time, especially when you are doing a job which people take turns to do, so that someone is always doing it He’s on night duty. Mary goes on duty (=starts working) tonight at half past ten. What time do you go off duty (=finish work)? → duty
Examples from the Corpus
go off duty• Emil, the chefs, Oliver and Cathy had finished cleaning up and had all gone off duty.• Debbie should be going off duty but decides to stay and see it through. 5.00 p.m.• The woman who answered said she thought Sally had gone off duty but would put me through to the staff quarters.• Called to identify the body just before I went off duty.• I had no doubt they'd turn up within a short time, so I went off duty.• Alice waited in the Stoners' living room while Lester got his instructions from Mrs Miller before she went off duty.• A doctor came, and said the same thing, then she went off duty for lunch.• The prison is locked up, the inmates are counted and the main staff go off duty. 