There wasn't really any evidence provided in this article that the late-start cities 'sleep in'. Perhaps people in SF just enjoy a leisurely breakfast on the balcony, watching the Sun rise, rather than rushing into the office?

Personally I have to be up at 05:30 to take care of the dog / kids / housework / exercise / have some personal time but don't start work until 11:00.

Better to have the bright mornings to myself than the dark evenings when I'm tired.