Just as a reference, from some posts that I undeleted just now:
In August 2017, in Multiple new devices trying to OTAA - #17 by kersing one of the developers wrote:
In December 2017 some timing was changed from 800ms to 1000ms:
I don’t fully grasp the code that handles this.
And dating back to April 2017:
@kersing, is this still valid, and do you think that TTN would know that the gateway has such queue?