I'm going to be spending time on VoK with the intent to figure out wtf is going on with the mission end timer.

I'm beginning to speculate that the end level trigger may also have something to do with the amount of enemies you have destroyed after the troops have made their way to the Star Destroyer.

I plan on testing this out with a profile w/ the homing cluster missiles upgrade and the cluster bomb upgrades to make quick work of the star destroyer defenses and ties. I will also try to be keeping a closer eye on the rebel troops to figure out if and where there is a trigger spot for the troops to end the mission.

Feel free to offer theorycrafts on what could be done to make this more consistent.

Well, I'm 99% sure it's the rebel troops reaching to a certain point that causes the level to end. Messed around a whole bunch off-stream and found a few curious tid-bits:

1) Destroying enemies doesn't have any effects to timing that I could tell, I did about 10 runs today and I couldn't get one to crack bellow 8 minutes using the flying car with cheats and homing cluster missiles.
2) If you pick the Y-Wing as your starter ship, you can actually just go straight to the cargo hold before the transport lands and blow it up! It doesn't seem to effect timing though, since cut scenes do not add to the in-game timer.
3) Rebel troops will shoot at nothing, and claim they're being shot even when no one is shooting at them
4) Lag might play a small role in timing, but when I tried to play a few runs with as little lag as possible when bombing the AT-PTs, and then flying around, looking at the sky as much as possible to reduce lag, I actually got my 2 worst time of 8:39 and 8:30
5) You can't bomb AT-ATs to smithereens 🙁
6) Destroying the guns to the star destroyer does not seem to effect the speed that the rebel troops reach their checkpoint.
7) I was consistently getting AT-ATs down at relatively the same time (within 3 seconds most of the time), but my final time still varied significantly.

I believe the key to cracking the code to this level is figuring out what causes the troops to go reach the final checkpoint the fastest.