[knc1]

Do not try to "catch" the correct time to press the key - you are already too late when you see the message.

Power on the device, as soon as you see the very first characters output, press AND HOLD the key until you get the prompt.

= = = =

Notes:
*) Do not load the "main" kernel in the "diag" memory place.
*) Do not load the "diag" kernel in the "main" memory place.
They can not be interchanged.

*) Do not be concerned about running the "diag" system, you do not need it.
In fact, you could forget about ever loading the "diag" system (unless you plan to screw up the "main" system in the future).

*) The only things that you need to install with fastboot is the u-image.
It is the u-image that contains the menu you need to continue the recovery (just use it to load the Amazon image of your choice).
*) Export USB
*) Transfer Amazon image to topmost level of visible USB storage.
*) Reboot
*) Done.

You are way over-thinking the problem, it really isn't rocket science.