USNA commits to informing everyone by April 15 as to their status: accepted, waitlisted, turndown.
As a general rule, most acceptances go out by the end of March and most of those who are notified in April will receive turndowns or waitlist letters -- just being honest. That said, there are always some who receive BFEs in early April and, as has been detailed on these boards, quite a few people are getting good news this week.