Depends on which island. Oahu or Guam?

Back when I worked at IRS the "big secret" was that the Service Centers didn't start looking at postmarks on returns until the week after the filing deadline.  I think they might have looked more closely at extension requests, though.  Of course that was back when Bob Newhart was still in his 40s and doing a network sitcom with Suzanne Pleshette (1937-2008).