get the amount of second to specific date php code example

Example 1: php start of day epoch

$beginOfDay = strtotime("today", $timestamp);
$endOfDay   = strtotime("tomorrow", $beginOfDay) - 1;

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();
?>