Our oaks seldom move in the afternoon. Come to think of it they don't move much in the morning either. They're always in the same place they were when I left them. Lol. Just joking. If you have acorns, especially white oak, the deer will eat them. You could kill them any time but think of it this way. When you go in pre-dawn you could have deer feeding on them then and run them off. They aren't likely to return that day and if done enough times, maybe not at all. If you go in for an afternoon hunt they aren't likely feeding at that time. Climb up and wait for them to show. I'm guessing afternoon would up your odds.