Captive portal, a way for users to keep track of their time?

[rhy7s]

I just have a splash screen set up on the captive portal but was just wondering if there would be any feasible options for users to keep track of their time connected? eg A simple timer on the logout pop-up or something that kept track of their MAC address over time, maybe using data from the captive portal log which could give them an idea of what they used in their last session next time they logged in? Would this be something worthwhile pursuing within pfsense?