It's an understandable question. I've asked it of artists myself in regards to a certain work. How long does it take to make a picture? How long does it rain? Every picture is different.
Two legendary songwriters, Bob Dylan and Leonard Cohen are sitting at a table in a cafe conversing about song writing. "I like that song you wrote called Hallelujah," Dylan says. "How long did that take you?" "Oh, the best part of two years," Cohen said. They started discussing Dylan's song called I and I. "How long did it take you to write that?" Cohen asked. "Ohhh, 15 minutes," Dylan responded.