Bob Dylan was famous for composing a song in a matter of minutes. It is said that he used to write two lines on a piece of paper and go to studio. Then and there he used to make up lyrics as he sang along. That is his genius.
For me, every song takes atleast a month that’s because I am a slogger. However, the day after my Dad expired, I got the tune and lyrics all in one shot in a matter of fifteen minutes.