Concerning how long it took Dylan to write a song, I like this story:

David Remnick’s stellar profile of Leonard Cohen in the New Yorker repeats the well-worn tale of the time that Bob Dylan asked him how long it took to write “Hallelujah.” “Two years,” he told him. “I really like ‘I and I.’ How long did it take you wrote that?” Dylan told him a mere 15 minutes. As Remnick pointed out, it actually took Cohen five years to write “Hallelujah,”....