If I gun for someone I will stick it out, (basically to the point of clear skies in a friendly sector when someone almost to final approach).
One thing though I don;t dig is when Im gunning, and the pilot doesnt have a microphone. Communication is key in this game.
I also dont enjoy the person taking over a gun position that im occupying. If you requested a gunner, then fly the plane, and stay out of my gun positions.
I also very rarely ever take a gunner in my own planes. No need to explain why.