Back when I used to bait, the big bears that would hit my baits were all nocturnal, regardless of the phase of the moon. I've always thought that hot weather was a factor as well with their being nocturnal. That said, as winter approaches and they're still trying to put on weight for the big nap, they don't have the time to restrict all their feeding to only night time, and as it got later and later in the season, I'd see more and more bears during the day on my baits.
Course, back in those days, lots of guys were running their hounds of mine and everyone elses baits. Those could be pretty tense times, but that's another story. The point is, the hounds really kept the bears on edge, and I think that was another factor for their being nocturnal...
That's been my experience....Jeff