Time tracking of activity on development VMs

Hi,
I’m a freelance developer with multiple clients. For each client I have a separate VM that I do the development on, and therefore I can tell if the RDP session into that VM is active, then I’m working on something for that client.
I think Grindstone almost does this for me, but I really don’t want to be bothered by it asking me where I’ve been every time I come back. I’ve got multiple monitors and sometimes I don’t notice the notification on the other monitor and I don’t think it counts the time until I click OK in the dialog with the “resume timing” option. I’d like, but can’t find, an option to silently track the active time of the machine without having to do anything each time I come back to it.
Thanks,
Richard