- var_dump: documentation ( source)
<?php
$tz = new DateTimeZone('America/Los_Angeles');
$now = new DateTime('now', $tz);
$twoDaysAgo1 = new DateTime('-2 days', $tz);
$twoDaysAgo1_1 = $now->sub(new DateInterval('P2D'));
$twoDaysAgo2 = new DateTime('-172800 seconds', $tz);
$twoDaysAgo3 = new DateTime('@' . ($now->getTimestamp() - 172800), $tz);
var_dump($twoDaysAgo1->getTimestamp());
var_dump($twoDaysAgo1_1->getTimestamp());
var_dump($twoDaysAgo2->getTimestamp());
var_dump($twoDaysAgo3->getTimestamp());