You should consider the possibility that you are wrong.

As I understand it, Henry Ford chose a 40-hour work week because he found that it maximized the total output of his employees. Computer programming is (minute-for-minute) considerably more demanding than working an assembly line. Maybe an average programmer maximizes her total output when she works substantially less than 40 hours a week. In fact I'd be surprised if that weren't the case.

And of course you could still run the service if you guys worked four-day weeks. Just make sure somebody's working on any given day.