My work day is 9 hours (with a 1 hour lunch). I track my time and find that about 25% is spent taking breaks from 'working'. The path of lease resistance for me is to work for 45 minutes and then take a 5 to 15 minute break to walk around the office, check HN, get coffee/water, etc.

So yeah about 6 hours of 'working' on an average day at the office for 9 hours.