There was a particular buck I hunted last year that acted like this. I have hundreds of pictures of him coming out in the same field every single night for weeks. Never once did he ever show himself during the day. The older mature bucks seem to go pretty much nocturnal. I don't know if its from pressure because they don't really have much around here. The buck I shot Saturday only came out during the day once over the last few weeks. I happened to be there that day. Most of them slip up eventually but its not often. You just have to be there when he does.