Immutable (new in PHP 5.5):

<?php
  $ts = new DateTimeImmutable("2019-05-30 10:30:59");
  $new = $ts->modify("+2 days");
  echo $ts->format(DateTime::RFC2822), "\n";
  echo $new->format(DateTime::RFC2822), "\n";
?>
Output
Thu, 30 May 2019 10:30:59 +0000 Sat, 01 Jun 2019 10:30:59 +0000