Cookie session expire

<?php 
// don't cache this page: 
header("Cache-Control: no-cache, must-revalidate"); 
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); 
// check for cookie, then set/refresh it: 
$asite = isset($_COOKIE['asite']); 
setcookie('asite', 1, time()+60*60, '/', '.mysite.com'); // note leading "." for domain 
// if cookie set, redirect: 
if($asite) 
{ 
   header("Location: http://www.mysite.com/page1/"); 
   exit; 
} 
// rest of intro page follows.... 
?>