I’m assuming the Christopher Reeve films from the '70s/'80s were not canon or very accurate to canon.
However, in the first classic film, Superman: The Movie, we see that he spent approximately 12 Earth years in the Fortress, learning from Jor-El.
What is the canonical amount of time (in the original comics) he spent at the Fortress becoming Superman in his early years? Were the Reeves-era films accurate in this regards? Or is the real time in the original comic canon far different?