I agree with ED, it will be done shortly after selected. If I recall correctly there is a definite due by date. I believe you must have the appointment made within 45 days of selection. Key words are the appointment made, not have had the apptmt. Caveat this is for HSSP, I don't know for ISSP.
They will send you a choice of DoDMERB docs that you can go to, but it is up to you to make the appointment. If you are a military brat you can go to your base doc, at least that is what we did for our DS in AFROTC.
You will go to an eye doc and a generalist, so be prepared to go to at least 2 docs. The docs will fax the paperwork into DoDMERB and it can take up to a few weeks to find out the results.
As ED stated don't delay this because you can not receive a penny until you are medically qualified, thus if the waiver doesn't come through for 6 months, and you don't have the physical until March, but school starts in Aug. That stipend won't come until later. They will back date it and you will get it, but it is a pain in the arse to work with DFAS to get it fixed.