This isn’t really rocket science.
There are plenty of videos out there of this - several of which show exactly the point when the first five or six single shots are heard, followed several seconds later by the first volley of full auto fire.
Some of these videos probably have an exact timestamp from the phone in the metadata. You’d probably need the original video - but it’s there.
Do some math and *bingo* you have the exact time the shooting started.
But you may never know the exact timestamps on any of the hotel audio/video...
When were the windows breached?