[Plugin: WordPress PopUp] Set Cookie Expiration Date on Pop Up

I got the premium version of this from WPMU, now I don’t have a paid account, so I’m posting here to see if I can get some help. I’m trying to figure out how to change the expiration date for the cookies on the pop up. Right now it’s set for over a year, which means people will never seen the pop up after they’ve seen it. I’d like them to see it in a month or so after they first saw it. Thanks.

http://wordpress.org/extend/plugins/wordpress-popup/