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.