3 Answers
Yes. You can get another 4 hour lab, then another, then another. I do it all the time! But each one is a brand new clean lab.
The correct link is https://labs.play-with-k8s.com/
I have raised a feature request to be able to save and restore your session at the play-with-k8s github repo, hope it gets noticed and someone works on it.
https://github.com/play-with-docker/play-with-kubernetes.github.io/issues/41
I believe you will be able to create the 4 hour sessions as many times as you want.