I don't see going nocturnal as being a way of maturing either. You can just as many pictures of the same buck showing up during the day and night. A friend of mine from North Dakota had tons of pictures of this buck that aged around 5 1/2 years old with a great 160 inch rack to boot. He showed up during the day and night and pretty much the same amount too. Mature bucks can go nocturnal because of hunting pressure or too much human precense in their area.