A "normal" photo period would correspond to...the sun? I guess the arguement could be made that any increase in down time for most people would be of benefit. On carb cycling, most places other than california (I'm in seattle) have little or no carb sources available during the winter unless it is being stock-pilled which may or may not be paleo. It is pretty clear that insulin resistance and fat gain would have been adaptive in the past when winter food consisted mainly of fat and protein from animals.