It is the individual only who is timeless. Societies, cultures, and civilizations -- past and present -- are often incomprehensible to outsiders, but the individual's hungers, anxieties, dreams, and preoccupations have remained unchanged through the millenia.
In the earlier novels, Steve King tells us that John Farson, and perhaps even the Crimson King himself, are but other names and faces that belong to Walter O'Dim. However, in The Dark Tower, he tells us very clearly that Walter, John Farson, and the Crimson King are actually separate individuals.