During the peak of the does' estrus cycle when they are about or are ready to be bred, any time of day is a good time to be hunting for a love struck buck. Over the several decades that I have hunted deer in the deep south, by far my most successfull time for both does and bucks has been later in the afternoon from about 3:00 p.m. to dusk. I have not had a great deal of success in early a.m., but those bucks that I have killed around 08:30 or earlier have been nicer ones. Why I have no clue.
I have had some nice bucks come crusiing by mid-day. Usually early in the season when the bucks are still in groups of 2-3-4-5. I cannot prove this, but seems to me that as the season progresses the mature deer (both older bucks and older does) where I hunt tend to become more nocturnal and if they do move in the daytime, it is 10:00 a.m. or later, on up to about 2:00 p.m. Trail camera evidence reinforce this notion. I have often wondered if they become somewhat conditioned to when most of us leave the woods and head in ?!?