How to increase days for user to sign up?

Hi, can you tell me how to increase the amount of days that a user can use his invitation before it becomes invalid. I would also need to update other areas to the email stating the how long the invite will be valid etc etc.

I noticed a lot of areas where it might change the time limit but so far I am having little luck in making the correct edits to not only increase the days but to inform the user in the email sent and when they attempt to use an out of date email (which I am assuming it does tell them it’s out of date)

http://wordpress.org/extend/plugins/wordpress-mu-secure-invites/