After your application is approximately 50% complete the SA will initiate the DoDMERB process. (I am not sure when the ROTC programs initiate DoDMERB)
From DoDMERB
https://dodmerb.tricare.osd.mil/FAQs.aspx
2. How do I schedule a DoDMERB physical?
Applicants for 4 year ROTC programs or guaranteed 3 year ROTC programs (normally applicants still in high school) will be forwarded by the respective programs to DoDMERB AFTER preliminary screening by the program has been completed.
A zip code search will be conducted and will “assign” an applicant to the nearest facility. It may be a Military Treatment Facility (MTF) or a government contracted civilian facility (Currently the contract belongs to Concorde, Inc., Philadelphia, PA. Concorde subcontracts out to a number of physicians, optometrists, and in some cases, audiologists, across the country.) In that case, it may be a physician and optometrist in two different locations, but relatively close to each other.
Applicants DO have the flexibility to determine where they would like to get their exams. Currently about 95% of examinations are completed by our contractor. Access to MTFs has been difficult with increased security requirements at the installations around the nation. Applicants generally wait much longer period of times for an appointment at an MTF versus completing their examination at our contractor. DoDMERB has no control over cancelled appointments at MTFs, secondary to deployments, etc.
a. The majority of the applicants will be scheduled with Concorde (DoD Contractor). They will receive a scheduling package in the mail with complete instructions along with the names, addresses, and phone numbers of the authorized examining physicians in your region.
b. The few applicants who will be scheduled at MTFs will receive a post card in the mail and be asked to call 1-800-841-2706.
c. Applicants “in college” will have their ROTC Detachments/Battalions coordinate the scheduling of their exams.