how to get seconds in x hours in php code example

Example 1: php redirect in seconds

header("refresh:5;url=wherever.php");

Example 2: add seconds to datetime php

<?php 
$date = new DateTime();
echo $date->getTimestamp(). "<br>";
$date->add(new DateInterval('PT674165S')); // adds 674165 secs
echo $date->getTimestamp();
?>