Time of day depends on my mood, and obviously theirs.
In KS, we can call 24/7, if I have a weekend totally free, I might call all day long, or if the moon is out, I might call all night. I'd rather be calling empty sets than sitting on the couch. Dusk and dawn are generally the best, night is very productive, midday generally sucks, but that's not to say you can't get dogs in all day.
When guys contest call, they'll run 20-30 sets during daylight hours, all day long.
Pressure fronts, warm fronts, chills, snow, rain, moon phase, etc etc, all can effect their movements. The way I figure it, I'd rather be calling than not.