I am heading to Manitoulin Island tomorrow for my second rifle hunt and my experience with apples is this. I usually lay out a dozen or so a few days before the hunt and they usually get hit right away, but for some reason as the week goes on, probably human scent, the activity at the apples slows considerably.
Last year I put out a bunch of apples on the Saturday before the hunt, had trail cam pictures of him at the apples Sunday and then nothing. I ended up harvesting him on Tuesday of the hunt but he was not coming to the bait when I shot him. As mentioned I think they will work better early season