Here is a quick video of how the time locked key code works.
Once you have specified the number of minutes, they will appear in the lower application bar and user will be able to see how much time left for him to work. Once all time has elapsed, it will close the session forcefully (if the user didn't do it already).

Here is a short video of how you would use a simple black and white list and how users will see it in the locked mode.