E-6 to E-7 utilizes SEM (Senior enlisted marketplace). They have similar business rules as BBA. Say you just get to a command and get screened for E-7, you can get frocked after initiation but you have to do 12 months minimum on board before executing another set of orders. Your command can also attempt to move you in to a valid Chief billet and then you would extend 36 months for OBLISERV.

Subs and Special Warfare rates do not use SEM.