This sets, in milliseconds, the maximum interval after which the device sends an APS message unconditionally regardless of whether any new triggering event has occurred, functioning as a periodic keepalive/heartbeat for the APS protocol session with the far end. This ensures the far-end peer continues to receive fresh APS state information even during long stretches with no status changes, which matters for detecting a broken message channel versus a genuinely stable, unchanged protection state. For example, setting this to 60000 (60 seconds) means even if nothing changes, an APS message is still sent at least once a minute so a silent transport failure can be distinguished from simply nothing having happened.