This is the time, in seconds, after which a pinned fault, one being kept visible past its actual resolution as referenced by the fault holder's pinning-cleared field earlier, automatically has its pin released. This controls how long a resolved-but-pinned fault stays artificially visible so an admin has a fair chance to notice it before it's allowed to disappear on its own, balancing visibility against not letting the fault log accumulate resolved noise indefinitely. A pinning expiration interval of 900 seconds, 15 minutes, means a transient fault that's already cleared will still show as pinned for 15 minutes after clearing before that hold is automatically released.