The closing ceremony is done after everyone is completed. So, yes the 8 lappers wait for the 20 and 30 lappers to complete. It's not as bad as it sounds - it only takes 35 - 40 seconds to complete a lap.
I'm not sure if it's common, but there were only 3 people in my group of 17 doing more than the 8 lap experience. And, the people who work there are very friendly and easy to engage in conversation to pass the time away.