So, sign me up for a 6 hour day and you'll get my full attention all day. I won't "need" to spend time on HN or twitter or whatever to kill time because I'll be fresh enough to work all day.
Also, because i believe there is a hell of a lot more to life than work, we'll work 4 days a week.
A guy can dream, can't he?
After about 7 hours of coding, I feel my code starts slipping off. Also, I code better at night. I know people who can't code for more than 6 hours a day or their work gets shitty.
I usually code 6 to 7 hours a day, and I take my friday afternoon (or part of it) and night off. This sometimes means working just the morning and the first half of the afternoon, and sometimes means working until 4am on the Thursday and then not working at all on Friday.
I think when you have great people on your team, that love their work (Not their jobs. Their work), it gets eaasier. This people will do their best, and that can't be measured in hours. That's why a fixed schedule actually sucks and many, many people don't like it.
But if you add a preparation, commute, lunch-time, etc... you easily end up with only 4-5 hours of "recreation".
Now imagine you have a wife, kids, friends, side projects, maybe want to watch SICP lectures, learn some Haskell...
4-5 hours is simply not enough.
http://en.wikipedia.org/wiki/Eight-hour_day
So after 100-110 years, maybe it's time to come up with even more efficient work day? (But keeping the right direction).