- date_default_timezone_get: documentation ( source)
<?php
$d = new DateTime('@-21474836470');
$d->setTimezone(new DateTimeZone(date_default_timezone_get()));
echo $d->format('c');
echo "\n";
echo $d->format('U');
echo "\n";
$d = new DateTime('1289-06-27T15:58:22');
echo $d->format('c');
echo "\n";
echo $d->format('U');