As soon as the counter reaches 00:30:01 you can either quit the session and join the next one or refresh the page by hitting Ctrl+R and you’ll be connected to the next student automatically.

If you have a double session with the same student, you don't need to quit. You should just stay connected for the full hour but remember to submit 2 feedback forms (you can just copy and paste the information from one feedback to another but make sure you set the session goal correctly)