Open modules/Your_Account/index.php
find
Code:
function docookie($setuid, $setusername, $setpass, $setstorynum, $setumode, $setuorder, $setthold, $setnoscore, $setublockon, $settheme, $setcommentmax) {
$info = base64_encode("$setuid:$setusername:$setpass:$setstorynum:$setumode:$setuorder:$setthold:$setnoscore:$setublockon:$settheme:$setcommentmax");
setcookie("user","$info",time()+2592000);
}
This is the function to set the user's cookie. as you can see it sets the cookie for 2592000 seconds. Change that value to the one you want. More info for the setcookie function can be found at
http://www.php.net/manual/en/function.setcookie.php