The waitlist moves when the school has a seat to fill. Given that many schools make 2-3 times as many offers as they have seats, for some schools there is no need to go to the waitlist (and some anxiety waiting to see if the offers accepted exceeds available seats), and others will not need the waitlist until well after the CTE. That said, you can stay on waitlists for as long as you wish and turn down an offer from a school you committed to, in order to accept the offer made from the school that waitlisted you. As you can picture, this causes a cascade as someone turns down Hopkins when taken off the list at Stanford and then someone comes off the waitlist Hopkins to fill the seat vacated by the applicant going to Stanford and that requires the applicant to turn down Harvard.... etc