In over 40 years of hunting, I've seen them at all times of the day, never did find any pattern.
One of the dumbest bucks I ever shot came within 30 feet of the pickup while I was eating lunch. He didn't even flinch as I almost spilled hot coffee all over myself scrambling out to make the kill. Quickly finished lunch, moved the pickup over to him and field dressed him.
He could only have made it easier if he would have jumped into the bed while he waited for me to shoot him