“The He 162 V1 first prototype flew within an astoundingly short period of time: the design was chosen on 25 September 1944 and first flew on 6 December, less than 90 days later”
They did have to cut ‘some’ corners to get there, though. That Wikipedia page mentions that it used a highly acidic glue that would disintegrate the wooden parts it was intended to be fastening, that that caused problems on the first flight and a deadly crash on the second, but that it wasn’t considered important enough to hold up the production schedule for even a day.
Also, Nazi Germany had a few designs that took way shorter than that to go from idea to first flight. An extreme example is https://en.wikipedia.org/wiki/Heinkel_He_162#Prototypes:
“The He 162 V1 first prototype flew within an astoundingly short period of time: the design was chosen on 25 September 1944 and first flew on 6 December, less than 90 days later”
They did have to cut ‘some’ corners to get there, though. That Wikipedia page mentions that it used a highly acidic glue that would disintegrate the wooden parts it was intended to be fastening, that that caused problems on the first flight and a deadly crash on the second, but that it wasn’t considered important enough to hold up the production schedule for even a day.