It takes twenty years to become an overnight success.

The earliest close match in the provided material appears in a 1945 Hedda Hopper Hollywood gossip column, framed as a rhetorical question about Hollywood and credited to no one in particular. The line circulated afterward in entertainment and journalism, with later speakers adapting the number of years (five, ten, twenty, etc.) to fit their point.

The remark is a humorous way to say that public recognition often comes only after a long period of unseen effort; what looks sudden from the outside is usually the result of many years of work.

Who was it said Hollywood is the place where it takes five years to become an overnight success?

It takes twenty years to make an overnight success.

It took this boy twenty years to become an overnight sensation.

With fewer films being produced in H’wood, it now takes ten years instead of five to become an overnight success.