Baltasound,
In the UK controllers are legally obliged to comply with the fatigue limitations laid down in the CAP 670 (
http://www.caa.co.uk/docs/33/CAP670.PDF.). Take a look at Part D, Section 2.
Within that framework ATC units may work to any one of a number of shift patterns, depending very much on the size of the unit, hours of operation, and traffic flows.