Flask limiting user sessions by time

I have rather unusual task, so I would like to ask for a piece of advice from experts :)

I need to build small Flask-based web which will have build-in video player. Users will have to log-in to access videos. The problem is that I need to limit user by the amount of time they can spend using the service.

Could someone please recommend a possible way to make it work or help me to find a place to get started?