- var_dump: documentation ( source)
<?php
$date = new DateTimeImmutable('2014-05');
$date2 = $date->modify('first day of next month midnight - 1 second');
var_dump($date2->format('U'));
var_dump($date2->format('c'));
var_dump($date2->getTimestamp());
var_dump($date2->format('U'));
var_dump($date2->format('c'));