iannem.. The shift system is arranged to cater for the operational needs of the ATC Unit. Many of the NATS 24-hour units work on a 5-watch system, which is basically 6 days on, 4 days off on a continuous cycle. Night duties are incorporated but usually not more than two in succession. A typical pattern might be 2 x mornings from 7am to 2pm; 2 x afternoons from 2pm to 10pm; 2 x nights from 10pm to 7am. At units where there is little traffic at night some of the watch members will do day duties instead of nights and those day duties vary considerably from early mornings to late afternoons. It's a bit more complicated, but that should give you some idea.
Breaks are arranged so that no controller works for more than a certain length of time without a break. At busy units it may mean 1.5 hours working followed by half an hour break. Meal breaks are included in the shift times mentioned above.
A controller on maximum leave allowance working a 5-watch system attends work about 180 days a year, give or take a few days.