My theory based on the places I've hunted:

In the morning you are most likely to bump them or any other deer off the field as you get there. The most likely time they will be there feeding is before shooting light as they've probably been feeding there all night. During daylight hours, they usually aren't feeding as most of them just fed all through the night. Your best hope of catching one in the morning is parking a long ways off and slipping in, hoping one is standing on it as shooting light arrives.

In the evening, you are already in your stand when it starts getting time for them to arrive. They have been mostly bedded all day, so food could very well be on their mind. Early season they may be more comfortable and arrive earlier, but as the season progresses they seem to get later and later before turning fully nocturnal. Sightings in the evening of bucks really depends on other food sources and the pressure they've been under.

During the rut, you are probably almost as likely to see them in the morning on a plot as the evening. Sometimes they will feed, but mostly they will just be cruising.