Like Tyrannosaurs said ( http://news.ycombinator.com/item?id=2555785 ), it depends on the nature of the start-up. "thinking in the shower" might work when it is about finding solutions to problems (although kids are rarely that demanding as the shower is)! ...but for the technical part, where those solutions have to be implemented, well, 6 hours per day would be either "employee thinking" or just a "lucky"/"very well designed" model of entrepreneurship.