how to add 20 minutes intervals in specific time duration php code example

Example 1: add seconds to datetime php

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

Example 2: add hour minute in datetime in php

$minutes_to_add = 5;

$time = new DateTime('2011-11-17 05:05');
$time->add(new DateInterval('PT' . $minutes_to_add . 'M'));

$stamp = $time->format('Y-m-d H:i');