I could retire today and be very comfortable for the remainder of my days (I am 41) but man would life get boring. Even if I work on projects I haven't had time for and travelled to places I wanted to go there is still something about working day in and day out, with a sense of urgency and with a group of people to make something greater than you could do on your own that leads to a sense of purpose. I also think that if you are spending that much time covering your arse you are working for the wrong company. You should revel in doing quality work not in covering your arse.
I'm not sure what the happiness maximizing number of work hours is, but I'm fairly certain it's larger than zero. Even Moore's Utopia posited a six hour workday.