What was the longest time it took someone to write a book?

David Markson: David Markson spent over 20 years writing his experimental novel "Wittgenstein's Mistress." The novel, published in 1988, is a fragmented and non-linear narrative that explores themes of language, philosophy, and consciousness. Markson's meticulous attention to detail and his insistence on getting every word just right contributed to the long gestation period of the book.