Specify multiple passwords for pages / posts / custom post types. An expiration date can be set for each password.
The password is deleted from the database, so it is no longer attached to your post.
The plugin use WordPress cron feature to periodically delete expired passwords. Please make sure this functionnality is working on your WordPress installation. WP-Cron Control plugin is a good way to see what's happening with the cron.
In WordPress, a post is protected as long as it has a password attached. When all the post passwords have expired, the post is no longer protected. It's as simple as that. To keep a post protected, assign it a password without an expiration date.
Yes. After deactivation or uninstallation, your posts are still protected with the first password that was attached to each of them.
Be sure that the timezone is well defined in /wp-admin/options-general.php
Yes. Actually these actions are defined :