Final answer:
One must have served a minimum of 12 months of active duty after recruit training to apply for brig staff duty.
Step-by-step explanation:
The question pertains to eligibility criteria for applying for brig staff duty within a military context. To answer the student's question directly: to apply for brig staff duty, an individual should have completed a minimum of 12 months of active duty following recruit training. This is the correct duration as per standard military eligibility requirements for such a position, ensuring that the individual has adequate experience and understanding of military operations before assuming the responsibilities associated with brig staff duty.