Look at the refresh.auto.interval property of the single value visualization using which you can make your panel refresh automatically after certain period.
http://docs.splunk.com/Documentation/Splunk/6.3.0/Viz/PanelreferenceforSimplifiedXML#single
Caveat: setting refresh interval too low may cause use search quota to be full.
I am currently using this but this cause the whole panel to refresh. I am looking for a way for the values to change without the whole panel to blank out.