Fix

<?
$time_interval = 1;#In seconds
$max_requests = 2;
$fast_request_check = ($_SESSION['last_session_request'] > time() - $time_interval);

if (!isset($_SESSION)) 
{
    # This is fresh session, initialize session and its variables
    session_start();
    $_SESSION['last_session_request'] = time();
    $_SESSION['request_cnt'] = 1;
}
elseif($fast_request_check && ($_SESSION['request_cnt'] < $max_requests))
{
   # This is fast, consecutive request, but meets max requests limit
   $_SESSION['request_cnt']++;
}
elseif($fast_request_check)
{
    # This is fast, consecutive request, and exceeds max requests limit - kill it
    die();
}
else
{
    # This request is not fast, so reset session variables
    $_SESSION['last_session_request'] = time();
    $_SESSION['request_cnt'] = 1;
}

?>