strtotime will work that out. the dates are just not the same and all in us-format.
<?php
$e1 = strtotime("2013-07-22T12:00:03Z");
echo date('y.m.d H:i', $e1);
echo "2013-07-22T12:00:03Z";
$e2 = strtotime("2013-07-23T18:18:15Z");
echo date ('y.m.d H:i', $e2);
echo "2013-07-23T18:18:15Z";
$e1 = strtotime("2013-07-21T23:57:04Z");
echo date ('y.m.d H:i', $e2);
echo "2013-07-21T23:57:04Z";
?>