Cut off times ensure your customers have enough of a heads up that they can make it into class on time. Without a cutoff time your customers might receive a notification that they've been added 10 minutes before class starts, and they might live 20 minutes away.

To ensure they have enough time to make it in, set a Cut-Off time (ex. 2 hours before class starts): Click Classes > Schedule > edit the individual class or series, using the drop down menu to the right > Click 'Enable waitlist' and choose the cutoff time.

Ex. putting 60 minutes would stop adding & notifying waitlisters an hour before class starts. See this article for directions with screenshots.