Watchdog can actually kick-in even if the user's currently logged into the system-- it will unlock your machine (make it available to run farm jobs) after X minutes of inactivity (no keyboard or mouse input).
If that's what you want, it would work great.
To set the watchdog timeout to other than the default 30 minutes, there's currently no official GUI for it, but you can use the "qblock" command from the command prompt.
This will set up machine01 to use watchdog that kicks in after 10 minutes:
qblock --watchdog 10 machine01