Anytime between now and May. The SA has to determine if you are fully qualified. You may not learn you are the “slate winner.” Some will have noms, not be fully qualified, not be offered an appointment. Some will have noms, be fully qualified, and not offered an appointment. And other outcomes, including offers of prep.
You may want to refresh on the Sticky post at the top of the Nominations forum.
Admissions is building out the class according to their evaluation process and to meet other goals. Once they know they want to offer an appointment to a candidate, they figure out what nom source to “charge” it to.
For some detailed reading on noms, and how others can be offered an appointment from the same slate:
https://fas.org/sgp/crs/misc/RL33213.pdf