When you access a lab, you are sent to a page which might look like the following -
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Click "Start Lab" to create the lab. This might take a few minutes. Machines are provisioned, booted up, and secure access created to the services listed. After the machines are ready to be accessed, it might appear as follows - 

You can use the name of the hosts to access the services or select "End Lab" in the top bar to end the lab.

If present a session timer will count down to indicate the time when the lab will be automatically shut down. If you want to access the session, select "Start Lab" at any time. This will reset the session timer so you now have the full session time available.