I don't think many people work more than six hours a day. Most work probably considerably less, the fact that they are at work for 8 hours notwithstanding. If they could remove some of these inefficiencies and return the time to employees it would be great.
They wouldn't work for net 6 hours either. It's not like the exchange is 8 hours including coffee breaks, Facebook checking and staring at the ceiling to 6 hours pure net uninterrupted work. It's 8 hours with distractions to 6 hours with distractions.
There absolutely would still be distractions.
But possibly less per hour in a 6 hour day than an 8, and so still a more efficient. Some studies on this would be interesting.