I've often said to my boss he would get more out of me if I only worked until 12 or 1 every day.

I'm an early bird. I officially start at 8 but it's very rare that I'm not at my desk by 7.15 latest. I love having the best part of an hour just to get through stuff in peace (it's actually closer to 2 hours as most people start at 9). I organise any meetings on or off site for the morning unless a client is absolutely insistent it must be later in the day. By the time it gets to about 1 I have had enough. What took 20 minutes in the morning takes an hour in the afternoon. I'm still proven as the most productive person in the role I do but I'd be moreso if I could maintain my morning output to the afternoon but I lose interest.

Obviously there is not going to be an agreement to me working 5 or 6 hours a day but I can honestly say my productivity wouldn't drop off one bit if it was to happen. I'd go further and say it would increase, as it would if I went to a 4 day week because I'd have to be working at my best all the time I was in the office or on the road rather than having the time to basically sit about for 3 or 4 hours in the afternoon.