You know what makes me the most productive? Working when I have the motivation to do so, I don't mean "I only want to work when I want"..
But sometimes it'll be midnight, and you'll get that brainpower flowing for some reason (I tend to be a night owl)...
Thankfully my position is flexible enough to then take the associated breaks the following day if I need to, or just go home if I'm not super productive (meetings permitting anyway)