Typically, the review boards desire to evaluate a "set" of completed applications at one time. Thus, instead of meeting at some predefined period of time, e.g., weekly, daily, etc., they wait until USNA Admissions receives a certain number of completed application, say, 15, 20, or 30 applications.
The members of the admissions board for a given cycle are senior folks who have significant "day jobs" and crowded schedules.Thus, weekly versus bi-weekly -- a rolling board. Thanks for the great information.