Adding 4hrs everyday to the users

I need assistance from any one who has an idea. I need to restrict the number of hours a user should be up and browsing per day. ie, if a user is to be allowed access for say, 4 hrs per day for a month. Once this uptime limit is reached, the hotspot/userman should log the user out, and added another fresh 4hrs to the user on the next day.Am running user manager and hotspot on the same router machine