Slate winners are determined when the winner is clear. This will vary by district, the competition in any given year, and the other possible sources of nomination/appointment for the candidates on the slate. Also, it is possible that later in the process the appointment will be charged to another category in order to mold the class admissions wants.
The RC can see the status of applications in the pipeline and potential applications. Admissions is not going to determine a slate winner if there is a possibility that a stronger candidate would win once the application is completed.
In mid-January the application window has not even closed, so if two or more candidates are close and all applications are not complete, admissions will wait until a clear winner can be determined. However, if one or more of the candidates in question are 3Q and admissions determines that these candidates will be offered appointments whether or not they win the slate, admissions may make the offers and resolve the slate when the rest of the applications are complete.