- date_default_timezone_get: documentation ( source)
<?php
echo date_default_timezone_get(); // prints Europe/Amsterdam
echo "\n\n";
$dateTime = new DateTime('2016-10-29 10:00:00');
echo $dateTime->format(DateTime::RFC3339);
echo "\n";
$dateTime->add(new DateInterval('PT23H'));
echo $dateTime->format(DateTime::RFC3339); // prints 2016-10-30T08:00:00+01:00
echo "\n\n";
$dateTime = new DateTime('2016-10-29 10:00:00');
echo $dateTime->format(DateTime::RFC3339);
echo "\n";
$dateTime->modify('+ 23 hours');
echo $dateTime->format(DateTime::RFC3339); // prints 2016-10-30T09:00:00+01:00
echo "\n\n";