As said, very much depends on how much time you can dedicate to it, full time, should be no problem, though you can never guarantee the UK weather - 1/2 day/week then it gets harder, both from the view of more chance of disruption for wx and continuity. IMHO most people should be able to complete in 45 hours if not stretching it out too much, the hours go up when you lose continuity and have to go back over stuff. After September the wx generally goes downhill, so the more you can do at the start the better.