I have set the cookie for 7200 (I recently changed it from 3600 hoping it would solve the problem). I didn't post the code since I have other files such as the config and other includes so the cookie code may not make much sense but here it goes anyway I basically wrote it this way in case I ever wanted to change a cookie name I can and it also checks to make sure someone doesn't cheat by editing their cookie file by checking that all of the cookie values match those found in the DB. Here is part of the code for the login page:
if ( clean_var($_POST["login"]) && $error != TRUE )
{
$md5_pass = md5($pass . SALT);
setcookie($ck_admin_user, $user, time() + $cookie_expire_time);
setcookie($ck_admin_pass, $md5_pass, time() + $cookie_expire_time);
setcookie($ck_admin_level, $row['level'], time() + $cookie_expire_time);
header("Location: ".$site_url."admin/admin.php");
exit;
}
Basically just using the setcookie function. It always works in Firefox but sometimes it doesn't work in IE.