Ruskin said, "For all books are divisible into two classes, the books of the hour, and the books of all time." By this, he meant that some books stand the test of time and are classics, while other books are just of that moment.
In Fahrenheit 451, the books that Montag and the other firemen burn are books of all time, as their society has not produced books of the hour in some time. Montag recites to Clarisse, "Monday burn Millay, Wednesday Whitman, Friday Faulkner, burn 'em to ashes." These authors—Millay, Whitman, and Faulkner—wrote books of all time, as their works are classics that have stood the test of time. Later in the book, Montag meets a society of people that have committed books to memory, and these books are also books of all time, including Swift, Dickens, and works by great thinkers such as Einstein, Lincoln, Gandhi, Confucius, and Darwin. This secret society has thought it worthwhile only to memorize books of all time, as these are the classics that future generations should know. Fahrenheit 451 has itself become a book of all time, as it is still read many years after its initial publication in 1953 and discusses ideas that are still relevant.