Save this as timep.php, it is better that you put this timep.php on an iframe within your webpage so that it will run independently since it is reloading every few seconds
<html>
<head>
<SCRIPT LANGUAGE="JavaScript">
<!-- Begin
redirTime = "2000";
redirURL = "timep.php";
function redirTimer() { self.setTimeout("self.location.href = redirURL;",redirTime); }
// End -->
//window.onload="redirTimer";
</script>
<head>
<body onLoad="redirTimer()">
<?php
$datev="01/01/2009 10:25:22"; //desired date /time
$datep=date('Y-m-d H:i:s'); // current time
if($datev <= $datep) {
echo "call your function name here";
}
?>