Eh, it's comics. Definitely sounds like a throwaway line a random writer threw in there though.
I remember reading something about how the human body works best when we sleep for like 1-2 hours for every 6 that we're awake, right there and then, not at the end of the day like most people do. Which is one of the reasons that mid-day naps are really good for the body. Batman can actually use this technique as he can actually use it.