Gofer,
The reason it takes 10-15 seconds to transmit, is that the ACARS MU has to have a reception level from the ground station above a certain threshold for 10 secs, and it does not accuire the station, unles specially requested, on ground. I am SO impressed with your calculations, my humble experience with ACARS is only as a lowly engineer, and I KNOW that it takes 10-15 secs from the time you get the "message sent" cue on the cdu until the message apears on the reciver computer.
Anyway, itīs scary to reminiss about. It means that they had quite some time to think, 10 seconds is a long time to sit in a cockpit going 140 kts with no control.
God speed guys - RIP.
Brgds
Doc