I’ve only heard rumors regarding this; I also know that, since the US had poached so many German scientists, that the Nazi nuke program was slowed down quite a bit. But by how much?
More can be written, but you might like to start with the FAQ section "How close did the Nazis come to developing the atomic bomb?" by /u/restricteddata , especially the first two replies.
This is not to discourage discussion. More questions, data, and debate are welcome.