Here is how it works. You access the wifi and the system sees a new connection that is hasn't logged. On your first HTTP request (www.cnn.com etc...) the system sends you a login page (called a captive portal). You put in the code and the portal tells the wifi controller to allow you for 24 hours, start timer now. Your mac address is placed in the logs and the clock times down.

If you want to "reset" the connection you have to use another mac address, or you have to get the wifi managment company to pull your connection (good luck with that).

You can change your mac address, on some devices. Google "spoof mac address", that will probably get you directions.

I could probably engineer a way to resend initial captive portal settings, I have to look at the post transaction at one of these places with a sniffer and see if there is a start-time flag in the post. I will see if anything can be done, but I doubt it.