Delayed action?
 

The idea is to build a ground strafing mission, with fighter bombers attacking an airfield and defending AI fighters scrambling just while bombs begin to fall. In order to do this, I thought to use a "TPassThrough" trigger setting the range limit very close to the target, but in this way there should be an unpleasant effect of "materialization" of defenders seen from the raider's cockpit. So I wonder if there is any way to delay the action of the defending group, so that they can spawn on the runway at the "click" of the trigger, but take off only after a time to define; in this way I could set the trigger range farther.

one thing you could try, is to set spawning planes to 'spawn parked' thus they will then have to taxi to runway. this should give a couple of minute delay before they reach runway.

bit of a work around but might achieve something near what you want?

I tried, but fighters spawn inside the hangar (it's Lympne airfield) with engine off, and they need ages to reach the runway and take off. I also tried selecting both "spawn parked" and "scramble" but nothing changes.