Of course academic work is creative work, but saying "there's no off switch" is too simplistic. Academics are people too. They prepare meals, watch television, spend time with their kids and spouse, go grocery shopping, go out for drinks, and visit mindless entertainment websites just like the rest of us. They may happen to think about their work during those activities but ,if they do, it's only by accident. The question of how much time they spend in these "leisure" activities vs "work" activities is well-posed enough to have a useful answer. And of course it varies from week to week but that doesn't mean we can't talk about what the distribution looks like. A professor whose average workweek is 60 hours lives a different life than one whose average workweek is 40 hours.