Germany's nuclear program was a disorganized shit show. It wasn't even a program, so much as a funding source for various unconnected (and competitive) research groups.

The only way you get a German bomb before the Allies glass Alamogordo is by going a lot further back than the battle of France. Even then, I don't see how the Nazis don't chase out all of their best scientists, kneecapping themselves from the get go.