Thanks Bdale and Chuck for providing some of the answers!
> How do I reduce the heartbeat timing below three seconds?
    The CDNC hartbeat control is in two pieces: (1) the pulldown
    for changing frequency of the heartbeat and (2) the button
    to enable or disable the heartbeat.
    So: select the rate using the pulldown, then press the [Heartbeat] button
    to enable it.  If you want to change rate then press the button to stop
    it, adjust the pulldown to change rate, then press the button to
    enable it once more. 
    This help?