Programs like Georgetown, EVMS, Cincinnati and Tulane ACP support same-year apps. The way this works is that the student has all their ducks in a row (competitive MCAT, LORs, ECs, everything but GPA, plus they've probably applied before), and the SMP's dean sends out letters to med schools supporting their app, after the first semester of classes are done. For med schools that are familiar with these SMPs, there's some same-year success. But mostly the success is in the med school that hosts the SMP.
In pretty much all other cases, a postbac or SMP doesn't help a same-year med school app process at all. The interview season is all but over by the time any assets are available.
The "best of breed" SMP, Georgetown, places 50% of its students same year, and not many go into Georgetown. SMPs that have tight linkage with the host med school (EVMS, Cincinnati, Tulane ACP, Temple) are the ones that have 85% or better same year success.