I tried a win7x64 VADC (6.2 version) in my local setup. When I set the sessionTimeout to 10 in registry, it does disconnect my session after 10 minutes. The registry works fine in my local setup.
I copied the following instructions from VADC guide:
The registry values are located in the registry key HKEY_LOCAL_MACHINE\Software\VMware, Inc.\VMware VDM\Agent\Configuration\XMLAPI.
Name : Session Timeout
Registry key: sessionTimeout REG_SZ
Description: The period of time a user can keep a session open after logging in with Horizon Client. The value is setin minutes. The default is 600 minutes. When this timeout is reached, all of a user's desktop and applications sessions are disconnected.
Please confirm if 10 minutes setting take effect in your environment. I will do more testing with longer duration in my setup as well. For example, 800 minutes. But IMO, the registry only accept integer numbers as valid input.