Personally, I was more interested in having my hot-desk users automatically logged back in after an outage (generator test, etc...).
So I edited settings in - I think - Controller registry, so that hotdesk users would be logged back in after an outage.
I recently had to attend a site to move their controller to a new office. The users' phones were all packed away in crates, I moved the controller, and over the next 3 days, the removalists and IT people put the phones back on desks.
Imagine my surprise to discover that the phones logged everybody back in, even 3 days later! - that's almost 400 people who didn't log any support tickets about forgetting their PIN! Result!
I have no idea why you would want a phone to forget its user. But you should be able to do the opposite of what I did and make it less convenient for the users by changing whatever the time-out was that I changed in the Controller Registry.