How to Create a Client Login Portal in WordPress :: WP-Client
http://WP-Client.com :: How to Create a Client Login Portal in WordPress :: Time Limited Access :: Expiration Date for Users :: If you have the need to limit the amount of time a user has access to the private portions of your website, then you can optionally set their permissions to expire after a determined amount of time. Their user will not be deleted, but will no longer have access. Access can easily be reinstated if necessary.