ATCOs working hours are regulated by the appropriate aviation authority. I was an Aerodrome controller up until 4 years ago. An ATSU is able to combine the Aerodrome and Procedural Approach control functions provding it's not too busy, I'm doing area radar now so things may have changed but in those days, we wouldn't work more than 2 hours without a break of at least 30 minutes, this is inline wih SRATCOH (Scheme for the regulation of the Hours of Civil ATCOs in the UK) I think! You can view the entire Scheme for yourself on-line
CAP670 in Part D, section 1, but beware, it's 1.9mb! Would be intrested to know which European unit it was that you visited. Last time I went into a tower, was at Manchester, there were more staff than aeroplanes, must have been for the very new shiny piece of tarmac!!!
