We are a H24 non NATS unit, but we only have one atca per shift, and one on days, to cover between 0545 -2200.
The standard atca shift is, 0900 -1700 (days), 0545 - 1345 or 1345 - 2200.
A written agreement exists which entitles them to at least one 30 minute break, but if there is no day atca, more often than not, a spare atco will also be available to extend that to at least an hour.
The day shift atca will cover for leave/sickness, but otherwise they will give the am/pm atca a significantly early go or late start (this is an unwritten agreement).
Overtime for public transport flights is optional, but when it is worked, it is usually taken as time in lieu at the O/T rate, instead of cash.