Why are you not simply scheduling the exam vs contacting your counselor to determine how long you have to do it?
Frequently, the results of the DoDMERB exam identify issues/concerns. Some concerns require action as simple as a writing a letter, others require gathering additional medical information and/or tests, and others are a DQ which could possibly require going through the entire waiver process (which in some cases can be elongated). It is to your benefit to start the process sooner than later.
Take the initiative and get it done. Your competition is.