Private site – WordPress Access Control Manager – settings not saving?

I’m just installing Private! on a network of client development sites. The individual sites will be accessible only to their respective clients for review and collaboration until we’re ready to go live. …unfortunately, I’ve run into an issue within the first page of install instructions, which state that the site will be inaccessible to even the administrator until the access time is configured:

Under Users: “If you want to allow this user to access your Private! areas, edit this field to a date in the future.” — the date change will not save – and also, just in case, there is no explanation of what to do if it expires before you’ve re-set it.

I have WP version 3.1.3, with one sub-site so far, and I have no other plugins installed except the default akismet; I’ve tried setting the “future date” for both the super-admin and the admin user of the one sub-site.

Can anyone help out with this? Is there a method that’s less complicated — I simply want to restrict visibility of and access to individual sites within a network so that only users who I’ve authorized, via a login page, are able to view the site.

thanks!