Following are some of the dashnoard/panel refresh options. I am not sure as to how to make this refresh work only betwee 8:30 to 5:30 PM.
1) Refresh entire view on periodic basis (following is for every 5 minutes)
2) Individual Panel auto-refresh
(i) Splunk Enterprise 6.5 onward. Create your Search Panel and edit the search to add Auto Refresh Delay or do the same via Simple XML for specific Search Panel add following code
(ii) refresh.auto.interval to refresh individual panel (deprecated feature now, however you can use the same in case you are using Splunk Enterprise 6.1 or greater but not on Splunk 6.5)