You should look outside the box. . . .
In some OSOs, MEPS is local, going to a Naval Hospital (or other appropriate facility) is not too feasible, especially while school is in session. So, a "aviation candidate" physical can be done at a MEPS station and it can guarantee you a flight slot with HQMC before attending OCS. It's more of a geographic convenience thing . . as far as how it is done.
My point about TBS physical is that many SNAs were given throrough flight physicals (regardless of when the last one was) at TBS to make sure 1) you didn't have any reason to compete for a ground MOS 2) avoid a long one at API. Because we got thorough Quanitco physicals, some of us spent 30 minutes at NAMI Pensacola rather than 7 hours.