I am using a cookie on my site to display colorbox one time on page load then after that the user has the option to manually load the colorbox each time. But what I do not understand is how you set the expiration date for the cookie. I got the needed code from [another question](https://stackoverflow.com/questions/6086984/using-cookies-to-load-colorbox-on-first-page-load-only) here on SO and it would help if someone could explain to me what is what here.

```
var $j = jQuery.noConflict();

$j(document).ready(function(){

   if (document.cookie.indexOf('visited=true') == -1) 
   {
      var fifteenDays = 1000*60*60*24*15;
      var expires = new Date((new Date()).valueOf() + fifteenDays);
      document.cookie = "visited=true;expires=" + expires.toUTCString();
      $j.colorbox({ inline:true, href:"#gallery-nav-instruct"});
   }

});

```

I would assume this means the cookie expires in 15 days. How would I change this to longer? Say 30 or 60 days?