I am trying your plugin out and when I set the time for a user's password to expire (say today at 12PM). I'm on the East Coast and my WP site is set to use New York Time. When I set the expiration date to 4/12/2013 at 12:00 and hit save, the user's password is immediately set to expire even though 12PM EST hasn't happened. What timezone is the plugin using? UTC?
I also am not getting either an admin notification or a user notification when a user's password expires. Is that because the expire date/time has already happened? I am able to get other emails form my WP site and I am able to schedule future posts on my site using the New York time.