Here in Arkansas in the Ozarks where I live the Agfc has planted a great number of food plots. It is not hard to tell which plots the birds are using. Just look for droppings,scratchings and dropped feathers.
I use the late afternoon to try to locate a bird on the roost for the next morning hunt. I use the same methods I would use in the morning such as the owl or crow call.
Best of luck!