But, that said, I'm surprised that no one has mentioned here that M-Th, 9-6 isn't a 4-day week, unless you include a required lunch hour, which most don't. So, since you didn't mention that, and I'm fairly sure that you work through lunch as many do including myself, then 9-6 M-Th is 36 hours, which is 4.5 "normal" 8-hour workdays.
I challenge you to be profitable working 32 hours a week (the equivalent of 4 8-hour workdays), preferably using flex time (so people can work those hours whenever they wish) and allowing telecommuting whenever the employee desires, and still be profitable.