To change the Ring-In Timer, click on the drop-down menu, and click on your desired time. You may also highlight the box and type in your own time values, in seconds:
The Ring-In Timer will start automatically after the Read Timer expires (or when the question appears on the screen, if the Read Timer is set to 0) and is displayed as a light colored bar at the bottom of the screen that gets shorter as time runs down:
The default setting for the Ring-In Timer is 15 seconds.