I don’t know the flight time of a torpedo, but I can look into it. That said, torpedoes are still most definitely controlled by a timer instead of a maximum distance. I tried manual firing some ordinance around a black hole to see if I could get the gravity well to slingshot it around and hit the target, but the missile timed out before it hit the target and well before it traveled 5k.
Edit: Shoulda just done the research first. Torpedo flight time looks like it’s ~18 seconds.