As the title suggests- the more realistic duration of the self-test sequence, initiated via pressing the "ЭКРАН ВЫЗОВ" button and executed with the presence of the "ЭКРАН ГОДЕН" message on unit 2Э in the cockpit, should be closer to approx. 3-5 seconds and not after 15, as in the "MiG-29A flight manual that is available on Amazon.com". In fact it's up to 15 seconds according to the technical manual (142.21.00).
This can be easily confimed by anyone (pilot or technician) who has ever started up an 9-12A aircraft, equipped with the ЭКРАН-03МЭ system, or as shown in this short video, featuring a Slovak AF MiG-29 (6278, originally a 9-12A) : https://youtu.be/up-b7lFBBqI?si=MzN7SHnReDB9-9m2&t=27.
If you play the video frame by frame from timestamp 0:27 you can observe the button being pressed, the "САМОКОНТ" and "ЭКРАН ГОДЕН" messages. Considering that the video speed might have been altered or video frames overlapped (doesn't seem to be the case), the duration of the self-test sequence is still way shorter than the 15sec that we have currently in DCS.
I suppose that introducing a random duration of the self-test, closer to the real one, will add a small touch, contributing the overall immersion.