And don't forget that at busy units the amount of time one actually spends working will be limited to maybe 1.5 or 2 hours before having a half hour break. So, although one has to attend "the office" for 7 hours, one might only work for 5. During winter months, when less people are on leave, it may be somewhat less.
I can't speak for nowadays, but when I worked at Heathrow and Terminal Control my attendances for the year usually amounted to about 180 days, so I got much, much more time off than some school teachers I know... and that really peeved them!!