It's odd, to me at least, that they seem to be assuming that sleeping once a day is biologically sound. I thought it was pretty well accepted that our biology supported the idea of sleeping twice a day (based on hormone level fluctuations throughout the day). The only reason we insist on sleeping only at night even after the advent of electric lighting and such is a sort of blind adherence to tradition combined with casual sadism practiced by everyone who gets to lord power over others (parents, employers, etc).