I'm sorry I keep posting I am not trying to hog this thread but I have a pretty concrete answer on the missing scene from the snowspeeders in the Hanger found via music cues.

This animation found in Jamie Bennings "Building Empire" @32.29 Is the missing 2.5 seconds that John williams scored the music to before seeing the AT-AT's attack.

I was mouthing 3 snowspeeders whooshing overhead and imagining they were going out the tunnel I got the number that were meant to be there correct in my imagination but I only just realized this is the shot intended and never filmed but scored and they are up in the air already and banking overhead going over camera.