I know this'll be a controversial stance but IMHO.. needing to work 5 or 6 days a week to prove the business case, make the business stick, and to scale the business to a point where you have multiple employees and processes that allow you to only work 4 day weeks if you want.

Of course, some businesses can run on fewer hours from the start, but many require a lot of sweat and long hours to get the engine running.