To the best of my meager knowledge, everything is set when the weapon or ability is triggered. In other words, anything that has an effect has its status checked at that time and that time only.
But Iv'e been wrong before. You could always just go fire a torpedo and come back and tell us all for sure.
Iirc, the hit or miss is determined when fired, as is the damage buffs.
But, the damage applied is determined when target is hit to take into account resists and shield level etc.
So, if a player launched Torps, then APA, and then 3 part omega as long as the grav anchor (a projectile itself) hits before the torps do than the debuff is calculated in terms of resists but the APA boost would not be since it was activated after.
As you know, but others may not it's why movement/defense debuffs should be applied to a target before firing on that target.
To my knowledge, I have found that oddly enough, with things like APB, the debuff is applied twice. First when the torp fires, then again upon hit. As for things like APO3 and APA3, I think it's as long as they are still active upon firing, they will stay with them even after they run out.
But it's best if tested.
It is said the best weapon is one that is never fired. I disagree. The best weapon is one you only have to fire... once.