Staff Service. Additionally, once during Phase III and once during
Phase IV, the cadet will participate in staff service, acting as an apprentice
to a senior member staff officer for 4-6 weeks (see Figure 1, page 3). To
fulfill this requirement, the cadet may serve as a staff assistant in any of
the staff positions associated with the Phase. For example, in Phase III,
the cadet may serve as a cadet flight commander, administrative officer,
or public affairs officer, under the supervision of the senior member
counterpart on the squadron staff. Which position the cadet serves in is
up to the squadron commander.
So could the cadet pass achievement 11,
and during the ensuing 56 days time in grade required for the Earhart, while passing the test,
serve 4-6 weeks in any one of the 3 positions, and check off the boxes for it?
Yeps.
I'm not sure that's the intent though, I always got the sense that the idea was that you do the 'staff service' for your phase, while you were working on that achievement. Of course there is no written requirement of that, and practically speaking, rarely actually happens that way.
I can tell you that I have never (would never) put C/Capt on a cadet who did not, in the course of their normally assigned duties during phase 3, more than exceed the requirements for staff service for Flight Commander (including giving the annual scholarship brief, hehh --amongst many others). Still a few of them chose (usually based on their own interest, to do PAO instead, just because, I guess)