When can cadets change into civilian clothing?

The correct choice indicates that cadets are permitted to change into civilian clothing prior to departing from campus. This policy typically aims to maintain a standard of dress while on campus grounds during the day, ensuring that cadets adhere to the expected uniform protocol. It reflects the formality and discipline expected in a military training environment.

Changing clothing before leaving campus allows cadets to signify their transition from a structured educational setting to their personal time, while still respecting the regulations in place during their time on campus. The timing is significant as it ensures that all cadets are presentable and uniformed throughout their scheduled responsibilities.

The other options suggest changing clothes at different times, such as before 1700 or immediately after last class, or after formations; however, these timings might not align with the established rules, which are designed to instill time management and respect for the uniform. Hence, the choice of changing prior to departing campus is the policy that best balances adherence to military protocol with personal choice.