sub TimeStamp {
  for ($_[0]) {
    if( /(\d{4})(\d{2})(\d{2})/ ) {
      #returns in MMDDYYYY
      $_ = "$2/$3/$1"
    } else {
      warn "Invalid input to TimeStamp()";
    }
  }
}
...
TimeStamp($date_created); # will modify $date_created