I'd agree on the music part. Timeless is something that stays unique, that will never be replicated. The Beatles have been successfully copied and mass-marketed, and are no longer really timeless. "Smells Like Teen Spirit", I would argue, is timeless, in that none of the imitators ever really pinned it down. Kids still hear it and it resonates with them. I would pin Queen as timeless as well, nobody has managed to really get that formula right again, but it still appeals today. Comedy can rarely be 'timeless', because its SO easy to steal a routine or a persona that made a previous comedian beloved, and thus dilute it.