According to General Order 5, under what circumstance can a sentry leave their post?

The correct answer emphasizes the importance of maintaining accountability and safety within the ranks. According to General Order 5, a sentry may leave their post only when they have been properly relieved. This rule is in place to ensure that there is always a watchful eye on the area being guarded, preventing any lapses in security that could compromise the safety of personnel, equipment, or information. A proper relief ensures that one sentry's responsibilities are transitioned seamlessly to another, thus maintaining vigilance and operational readiness.

The other choices do not align with military protocol regarding sentry duty. For instance, leaving a post due to feeling unwell can create gaps in security that could potentially lead to serious issues. Simply waiting for a set period or taking directives from an unauthorized individual, such as a fellow sentry without proper authority, can also undermine the integrity of the guard duty. Understanding this order reinforces the structure and discipline necessary for effective military operations.