- var_dump: documentation ( source)
<?php
$dateTime = new DateTimeImmutable('2018-06-26', new DateTimeZone('GMT+10:00'));
var_dump($dateTime->format('c'));
var_dump($dateTime->getTimestamp());
$dateTime = $dateTime->setTime(14, 0)->modify('- 10 days');
var_dump($dateTime->format('c'));
var_dump($dateTime->getTimestamp());