Wifi Hacking Question

Hi everyone,
I have a question about Wifi hacking.

Here is my situation as I was in the airport. To use internet there it worked like this:

First you connect to the Wifi.
Then, when you open a browser, a website open.
So you click on the webpage " connect to internet for free for 30 minutes " and a timer starts.

After 30 mins, I was thinking that if I make the "wifi" recognize me as a new machine, I could have 30 more mins.

Here is what I did:
(I'm running Kali linux)

So I tried to change my macc address with the command
macchanger -r wlan0
r is for random maccaddress and wlan0 is my interface (Wifi)

Then, I change my IP with the command
dhclient -r wlan0

It didn't work and I had to take my plane so I couldn't try anything else.

So I was thinking maybe when you connect to this internet they send you a cookie to make sure they recognize you and only allow 30 mins. Maybe by deleting that cookie, it would see the laptop as another machine and I could have another 30 mins?

What are your thoughts on this?

Thanks