I just finished reading Dr. Sheppard's book "Whitetails". According to his data it doesn't matter, 90-99% of feeding (depending on conditions) is going to be done at night regardless if its a corn pile or green patch. I know many here have read the book, for those who haven't-get it!!
Don't buy that number at all, lower the human pressure lower the percentage feeding at night. It's not the corn, it's not the wide open food plots, it's not the wide open hardwood timber that causes them to be shy in daytime it's the human pressure. IE pouring a bag of corn out every day or two and hunting it day after day, shooting alot in plots, over hunting stands, not hunting smart, riding 4 wheelers all over the property, game cameras in season, and so on.
