It is mostly likely timing based. It may well calculate how much time is left until collision, or perhaps until a 5G pull will become insufficient to recover. W

It is mostly likely timing based. It may well calculate how much time is left until collision, or perhaps until a 5G pull will become insufficient to recover. When that time remaining drops below N seconds (which from looks to be perhaps 1-3 seconds if it is the until insufficient time metric, or perhaps an extra few seconds for time until collision) it will activate. Obviously there are other criteria to prevent a landing approach from being seen as an imminent crash etc. But an override system that cannot be accidentally held by a disoriented or unconscious pilot seems plausible.