In 1/92 interview with the game's producer Shigeru Miyamoto published in the edition of Famicom Tsuushin magazine, he revealed that him and his team began developing the game at the same time as Super Mario World. Even back when they initially revealed the Super Famicom at the company in July, 1989, their plan had always had been to make and release the game alongside Super Mario World as a launch title for the new system. They were hoping to release the game in March of 1991, but it was delayed into the Summer, until it was finally released on the one-year anniversary of the release of the Super Famicom on November 21, 1991.
Contributed by ProtoSnake