I can't disagree more. Working 9 AM to 6 PM in San Francisco now will mean you get sunshine two hours from 7 to 9 (and that's assuming you get ready for work/play instantly). All the lovely daylight hours are wasted indoors.
Its not about what time you start and finish its about how long you work. Having an open ended working schedule is what is wrong with the work culture at most startups in silicon valley.