I do a 4 day work week as well, but they are 10-11 hour days
Like you, in actuality, I am working 24 hours, 7 days a week. The only difference is the location where I am working.
As a Software Engineer, some of my most brilliant innovations were created around 2:00 AM while at home. Heck, most of the time, while reading or postings on Free Republic!
My job is to create and invent new things to make our company profits. How and when that happens, even I do not know.