There is no good answer for this. Broadly, candidates, once they have a nom and are considered qualified in every other aspect, might receive an appointment in a window that goes up into May, and some cases, beyond. LOAs and principal noms, depending on SA (N/A to USCGA), also play a role. Some with a nom and fully qualified will not receive an appointment.
For an analysis based on reported USNA appointments to SAF, see this to get a feel for the appointment distribution timeline:
Class of 2021 USNA Appointment Thread
Note: <font color="#ff0000">(4) USNA Appointments on the 75th Anniversary of the bombing of Pearl Harbor !!
USNA Class of 2021 Appointments:
1) navyafgirl /(Self)/No LOA / Appt. Oct. 3, 2016 / Accepted ? / VA - POTUS / Presidential Nomination
2) Navymom2021/DS/No LOA/Appt. Oct.3, 2016/Accepted/VA - POTUS /Presidential Nomination
3) MCJROTC_is_cool/(Self)/No LOA/Appt. Oct. 3, 2016/Accepted/PA - POTUS/Presidential Nomination
4) Padre101/DS/No LOA/Appt. Oct. 24. 2016/N0t Yet Accepted/VA-POTUS/Presidential Nomination
5) GregInMD/DD/LOA/Appt. Oct 24, 2016/Accepted/MD/Senator Nomination
6) Navyboy17/(Self)/No LOA/ Appt. Oct 27, 2016/Accepted/KS/Senator Nomination
7) Johnathan/DS/No LOA/Appt. Oct 28, 2016/Accepted/NC/JROTC Nomination
8) USNAhopeful21/(Self)/No LOA/ Appt. Oct. 3, 2016/Accepted/NC/JROTC Nomination
9) Nav21/(Self)/LOA/Appt. Oct. 28, 2016/Accepted/AL-POTUS/Presidential Nomination
10) FloridaToUSMA2021/(Self)/LOA/Appt. Dec. 1, 2016/Accepted/FL/Congressional Nomination
11) USNA2021_Dad/DS/No LOA/Appt. Dec. 3, 2016/Not Yet Accepted/CO/Congressional
12) Sandra614/ DS/ No LOA/ Appt. Nov. 27, 2016/Not Yet Accepted/FL/Congressional
13) IRow2021/(Self)/ LOA/ Appt. Dec. 2, 2016/ Accepted/NC/JROTC Nomination
14) Schul542/ (self)/ LOA/ Appt. Dec. 7, 2016/ Not Yet Accepted/ IL/ Senator Nomination
15) Nosnow/DS/LOA/Appt. Dec.7, 2016/Not Yet Accepted/AZ/Congressional Nomination
16) laxer98/(Self)/LOA/Appt. Dec. 7, 2016/Not Yet Accepted/MD/Congressional Nomination
17) tmanbrin / self / No LOA / Appt. Dec. 7, 2016 / Accepted / CO / Senator Nomination
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