<!DOCTYPE html>
<html>
<body>
<?php
$winter=date_create("2013-12-31",timezone_open("Europe/Oslo"));
$summer=date_create("2013-06-30",timezone_open("Europe/Oslo"));
echo date_offset_get($winter) . " seconds.<br>";
echo date_offset_get($summer) . " seconds.";
?>
</body>
</html>