Germany was working on nuclear weapons, but as Nagel's book explains (
seem to explain, I still only know
that linked summary), that work was ineffective until 1942, at least partially due to quarrels between the involved
organisations and persons. There was some progress then, that led to a working, but not weapon-grade installation.
That seems to be the proven state of knowledge. The theme has produced public interest, especially after the German
reunification, as now some areas could be explored, that were more or less inaccessible before. And though there
were some headlines in the boulevard press about "sensational discoveries, that would change history", in the end
there was nothing, with regards to successful tests, or test sites.
If Germany would have had more, probably much more time to work on that field, and that means working
undisturbed (!), those scientists involved certainly could have designed a working nuclear bomb. How long
it would have taken then to actually build it, is just another matter ...
With the occupation of Germany all contemplable locations were investigated, because there still was the fear,
that Germanys research was more advanced, than it actually was, and the resources found, probably were included
into the allied stockpile, leading in some German circles to the question today, if Germany so wasn't responsible in
a way for the destruction of Hiroshima and Nagasaki ...
But without going to a 1946-, or rather 1947, 48, ... 50-What-If scenario I see no reason to believe in the famous
"German A-bomb", especially not, if we count in the actual proceeding of the war back then.