The
Hammer nutrition guide, which I find indispensable, says to have about 400 calories but not for three hours prior to the event. Their guide states if you eat before you go to bed, your glycogen is loaded, and won't be consumed during the night.
What I do is have my muesli concoction good to go in the refrigerator, and for purposes of hydration, drink a lot in the evening. Thus, I need to get up in the middle of the night for micturation, which provides an opportunity to wolf down the muesli at about 4 AM.