Dropping to 6 hours a day though is ... well, I don't know. I've seen those suggestions before too, but to me the problem is .. I'll never see my tank during the daytime hours then, except for maybe on weekends. It's not really something that appeals to me, don't know how others feel on the subject though, maybe I'm alone on this
Short of throwing the daytime cycle so far off the regular daytime at least .. I guess that's an option but then the problem is sunlight from the windows will interfere with your "daytime."
Maybe just enough white lights to give aesthetic appeal but not the most intense for the actual photosynthesis.