Take a look at
CAP 371. I'd guess for most airlines the crew will work pretty much the maximum permitted - factor in the typical sector lengths and you've got your answer.
As for Joyce's comments, the average person's 1800 working hours each year tend not to be done in the dead of night, weekends and public holidays. Nor does the average job have to be done right all the time.
On the other hand, maybe I'm a bit out of my depth on this one - I'm a simple controller. Shall we talk about having to have a break after an hour's work??