I heartily advocate that when it comes to managing their own time, employees do whatever they can get away with without getting fired. When it comes to negotiating compensation, companies exercise an enormous strategic advantage over employees, which they've proven completely willing to exercise in dishonest ways (cf. Apple/Google "non-poach" agreements). So when it comes to time-management, in the general case, I say fuck 'em. Get your work done, but when the door's closed, get out the clown suit and practice your torch-juggling routine if that's what you feel like doing.
Of course if you actually like your boss, or you don't think your company is run by dicks, and you'd feel bad about getting clown makeup on the company furniture, then don't do it. But only YOU can decide what's right in a given situation. No one needs employment morality lessons from business book authors.