interesting, in that from my perspective it's a joke that only works if you're reinforcing a cultural attitude that they're breaking a norm. I.e. it wouldn't exist or even thought to be said unless there was an inherent expectation/value in working long hours.

Also, I'd probably worry that such frequent jokes walk a very fine line towards passive aggressive behavior (again, such jokes just won't exist where there is no expectation).

obviously I don't know your workplace, so there's a good possibility no one gets offended, but just pointing out there's different interpretations of such actions, and just because no one's saying anything doesn't mean it's not happening...

(