We are home most of the time with our dogs and I can honestly say they are fast asleep on their beds between 8 and 4 and ignoring us completely. I can't say that their knowledge of our presence doesn't allow them to be so relaxed but they do spend a lot of time with their eyes closed

I think if you got it/them into a routine they would settle and sleep while you wern't there. I do know people that have them and work full time so it is possible.
Are you thinking of getting two dogs or just one? Two might keep each other company while your gone? They are great family dogs butI would probably be more worried about cats than sheep
Are you after a puppy or a mature dog (Rosie and Alice in Spain are looking for new homes)? Puppies of any breed are very high mantinance and would not take well to being left so much.. any chance you could take it to work with you for the first few months?
Hope that helps, probably more questions than answers:)