In my experience, 8 hours of face-to-face overlap actually makes me significantly less productive due to distractions. I can always get more done when it's more like 4-5, with 4-5 undistracted. Better yet is a remote work day. People can still contact each other via Slack, Mumble, Hangouts, etc.
> In my experience, 8 hours of face-to-face overlap actually makes me significantly less productive due to distractions.
In my own experience, those distractions are mostly due to open-plan and cubicle-farm offices. Given a proper one-man office, with a door, it's very easy to be productive.
It has the virtue of assuring that we are all available in person to one another, which is actually pretty valuable.