There were numerous reasons for the failure to accomplish anything in the German program.
First, the expulsion of all the Jewish scientists did leave a hole in their academic community, though they still had at least parity if not a mild lead in theoretical physics compared to us or the UK even after that.
Second, the guys who figured it could be made did not do a Hell of a job selling it to Hitler, so it was really treated more as a scientific prestige program rather than a war-winning weapon, and so was somewhat under-resourced (Becoming more so as the war progressed). Given that the program was never as tightly compartmentalized as the Manhattan Project (Only a tiny handfull of whose leaders knew the ultimate objective) there may be some credibility to speculation that some of the smartest players on their side figured out where it was going and it 'Spurred them on lesser efforts.'
Third, they were off on a totally unproductive rabbit trail with the heavy water reactors. Stupid idea, really; heavy water proved very valuable for unlocking the technology to make hydrogen bombs later on, but trying to use it alone to moderate a simple fission reactor is like trying to spin five plates on sticks while eating off of them. There is one way it can work right and a thousand ways for it to fail, nearly all of them more or less catastrophic.
The only way they could have been a year away would be to take what they had in 1945, and start from that with an entire new approach and priority level. Given that, yes, possibly a year. The way they were going, at least five.
