The timeout configuration is different for both vSphere Web Client & C# Client.
For vSphere C# Client take a look here http://www.virtuallyghetto.com/2012/07/inactivity-timeout-for-vsphere-c-client.html
For vSphere Web Client (which I assume you already know how to do) take a look here http://www.virtuallyghetto.com/2012/09/configuring-vsphere-web-client-session.html