As described in an earlier post on modifying the session timeout for the vCAC 6.0 UI you simply need to modify the following file on your AppD virtual appliance.
Edit the file
and find the following section
The timeout value is in minutes. Changing it to -1 effectively disables the idle timeout.
WARNING - always back up your AppD appliance when making changes. Also understand that this is not a supported configuration change so use at your own risk.