I don't have any data on this, but anecdotal evidence suggests that the average knowledge worker works 4 hours per days. So even if you're right, they're still doing 2x. When I have a programming/computer task a typical day for me is 8:30 am - 10:30 during weekdays. I work from home so there is no commute time and I usually quickly eat at my desk. If I have meetings and a lot of multi-tasking then that eats into my productivity because there's always task switching inertia.