When is a Sentry allowed to leave their post according to the Fifth Order?

A Sentry is allowed to leave their post when they have been properly relieved. This is a fundamental principle in military and security protocol, ensuring that the continuity of watch and security is maintained. Proper relief not only guarantees that the responsibilities of the guard are handed over appropriately but also ensures that the new Sentry is fully aware of any relevant information or situations that may affect security. Leaving a post without being properly relieved could lead to lapses in security or oversight, which is why this rule is strictly enforced.

The other scenarios, while they have their own significance, do not dictate the appropriate protocol for a Sentry's exit from their post. Completing their duty, receiving further orders, or being in an emergency situation may warrant attention, but they do not hold precedence over the requirement of official relief to maintain consistent watch and accountability.