Cookie expires with browser session?

I noticed that the cookie this plugin sets in Chrome is set to expire at the end of the browser session (haven’t checked other browsers but I’ll assume it’s universal). I have close to 500 posts in a photo-blog, and few people are going to go through all of those in a single session! I’d like to set the cookie to either not expire or at least keep track of what they’ve seen a little longer – so they can continue their exploration during multiple sessions…

Looking at the plug-in’s code, I don’t see where it sets an expiration for the cookie – but I don’t have much experience with cookie-code…

Anyone know how to do this?

http://wordpress.org/extend/plugins/random-post-link/