Actually, I did not misunderstand. Your comment here:
This is what I thought it was doing which is not what I want. I want to be able to specify n minutes after motion has stopped. However, I’ve been testing this and I’m not convinced what you describe is actually happening. More to come.
UPDATE: Okay, so it looks like new activations of a motion sensor does basically trigger the automation again effectively restarting the auto-off timer. But I do think the timer is from the start of the trigger, not when motion stops for eg. That’s where I was getting mixed up.