[bradknowles]

Each person is somewhat unique in this regard, but generally speaking there is a peak number of hours you can work and be effective. Beyond that, you're working longer and less effectively, and more likely to make mistakes. And that can be very counter productive.

On average, I think that number is about 6-8 hours per day for most people. But even that length isn't functioning at your peak, just high enough to be generally worthwhile. Peak effectiveness would be more like half that.

You need to do your research and find out what works best for you and your team, but the larger the group, the more likely you are to fall into the typical pattern.