Pro Plan users have access to configure SSL Certificate Monitors. This monitor was introduced to allow users of our service to track the validity and expiration of SSL Certificates configured on their domains.
You can only configure an SSL Certificate Monitor for SSL enabled websites. SSL enabled websites start with HTTPS:// whereas standard websites start with HTTP://
To configure an SSL Certificate Monitor, navigate to the Website that you want to configure the monitor on and then select Overview from the browse menu.
From this screen, if SSL has been identified on your server you have the ability to enable the SSL Monitor.
Also, be sure to check out the original SSL Certificate Monitor Blog post.