It's not possible with php as it's server side.
You can use javascript to refresh the page at set intervals and php will kick in again at that point.
-------- example of js reload ---------
<script language="Javascript">
function reload() {
location.href = 'page.php';
}
setTimeout("reload()", 300000);
</script>
Also, you can have variables generated passed in the QUERY_STRING as well.
hope this helps a bit,
-m.