The way a congressman/USCIS has explained to me, once your case reaches your FO, an officer will review your case to determine whether an interview is required. Therefore, once they are done reviewing what they need to review, they will either invite you to the interview or send you an RFE for medical (if you haven’t submitted it already/if the medical has expired). Basically, you just have to wait for the FO to contact you with further instructions.