As above . My Dad's station had four watches, they took in turns to do days, nights and late turns. 6 in the morn til 2 in afternoon , 2 til ten at night, 10 til six and one shift on changeover day ( not working ) There was an exception that if the appliance was 'dry' and had to return to base to recharge, changeover could occur then ( it would have to be a mega event for that to happen) he was based at an airport. They stayed til they were told to stand down from emergency.