The DoDMERB physical is good for 2 years from the date of the physical examination.
The academies and ROTC programs can only view their specific program, and they do not know what other programs you have applied for through DoDMERB.
Once you are in an academy or ROTC program you are out of DoDMERB's scope and will not be required to get another DoDMERB physical examination (unless you apply for the Uniformed Services University of Heath Sciences). You will be required to get a commissioning physical examination prior to graduation and commissioning. This is done by the academies and ROTC programs separate from DoDMERB.
Once you are on active duty will will be required to have a physical examination every 5 years. You may be required to have a physical examination more frequently depending on what specialty field you are in.