Thanks for your quick response, but this isn't answering my question. These are steps for setting the interval for when the system should timeout and require re-authentication. As the first article you posted says "You also can set a warning message that is displayed to the user whose session is about to expire." I am trying to find information, on where to configure this message. This message is prior to the actual timeout.
The default behavior is simply to timeout when the time you entered in the AG elapses. I've been looking around some more, I see a section called pzSessionTimerParams, which looks like this may be where the value is configured ootb. I cannot, though, find out where to access this screen. I'll continue to investigate and update here if I find anything.
I just tried to set 20sec as a timeout in mine AG.
After 20sec if I try to make any action in Developer portal (like open a rule) I immediately prompted with browser's SignIn modal window. It seems that in the response server sends a credential requests (and that's not Pega functionality, it is a browser's).