Script anti flood php

<?php
//
// Description : Script anti flood
// Version      : 0.0.1
// Auteur       : Atmoner <http://atmoner.com/>
// Url          : http://atmoner.com/script-anti-flood-php/
//
if (!isset($_SESSION)) {
    session_start();
}
// anti flood protection
if($_SESSION['last_session_request'] > time() - 2){
    // users will be redirected to this page if it makes requests faster than 2 seconds
    header("location: /flood.html");
    exit;
}
$_SESSION['last_session_request'] = time();
?>