In prior years, the class was filled within the first two weeks of May; after that, odds are diminishing.
Two (?) years ago they formally closed the list by June. They would only go back to the waitlist if someone still withdrew in the Summer (presumedly because she might have gotten off a waitlist elsewhere).
More likely it will be an intense period of in-person contacts, offering admission one-by-one, with a fairly short window to accept immediately.