What is time travel? John Lennon and Bobby Dylan were hanging around together around the time Dylan went electric (see Eat The Document). A song is not written the moment it goes to tape.
I won't say which (if either) is a derivative work but the opportunity is there that either could have heard the other's material in the formative stages long before the street date or public performance.
Paul McCartney dropped in on Brian Wilson during Sgt. Peppers'/SMiLE too.
Well, if I remember my Lennon/Dylan history properly, Dylan intended "4th Time Around" as a mock-up of "Norwegian Wood," although I could be wrong. Maybe Mr. Mojo knows...