- var_dump: documentation ( source)
- date_default_timezone_set: documentation ( source)
<?php
date_default_timezone_set("Europe/Amsterdam");
$date = new DateTime('2021-03-28 03:00:00', new DateTimeZone('Europe/Amsterdam'));
$_30mbefore = (clone $date)->sub(new DateInterval('PT30M'));
$_30mafter = (clone $date)->add(new DateInterval('PT30M'));
var_dump($date->format(DATE_ATOM));
var_dump($_30mbefore->format(DATE_ATOM));
var_dump($_30mafter->format(DATE_ATOM));