The “natural” explanation of his transfiguration is based on the well-established fact (announced by his personal physician) that Adolf Hitler suffered from a bipolar disorder. And on another well-established psychological fact that such a unique combination of talents (and of such magnitude) can only come from nature, not nurture (the latter can help develop them, but can not create them).
In other words, a man in question is born with these talents. In most cases, these gifts reveal themselves from the early childhood and grow slowly (or not so slowly) until the individual in question learns how to used them to achieve something really spectacular (i.e., do the work of a genius).
Depending on the specifics of these talents, the individual and the circumstances, this can happen just about any time – from the very early years (Mozart began to compose music at the age of five) to late teens, twenties and even later.
In rare cases these talents remain dormant until a shock or a sequence of shocks triggers them. And that’s what probably (very probably) happened in Hitler’s case.
The first two major shocks were his rejections by the School of Painting of the Academy of Fine Arts in Vienna. They were followed by a minor shock when he learned that he could not enter the School of Architecture because he did not have the required educational certificates (and could not get it due to his mental health condition – severe bipolar disorder).
But the decisive shocks happened during and immediately after the Great War. First he nearly escaped death a shell exploded in the dispatch runners’ dugout and was severely wounded in the thigh (spending two months in a hospital).
Then he was blinded in a mustard gas attack and for several days did not know for sure if he would be able to see again at all (let alone well enough to earn a living). Then he learned that due to the aftereffects of gas poisoning he will never be able to paint again (let alone become an architect).
Then came the humiliating defeat in the Great War (preceded and followed by the hunger of 1917-19), collapse of Imperial Germany, establishment of the Weimar Republic, Communists coups in Berlin and Munich. And, finally, the crushing and grossly unfair terms of the Treaty of Versailles (a genuine armed robbery of Germany and Germans).
If this explanation is correct (which may or may not be true), then his transfiguration happened right after June 28th, 1919 (the fifth anniversary of the assassination of Archduke Franz Ferdinand) when the treaty was signed by Germany and the victorious Allies.