I’ve focused on Time to Most Recent Four Alleles (TMR4A). TMR3A is just Time to Most Recent Three Alleles. This is computed as a genome-wide median. The justification is explained in depth elsewhere: Heliocentric Certainty Against a Bottleneck of Two? - #6 by swamidass.
I do aim to clarify this point eventually. It is going to be a harder explain to creationists, as population genetics is already just so non-intuitive. Still, I’ve wanted to understand this, and will be likely publishing on this soon too. It has has taken a lot of simulation work that I have not yet put in public. In the end, it is not that consequential, because it just pushes back the date from 500 kya to about 700 kya (or so).
There are many types of YEC. I know you don’t believe me. Just trust that I am not crazy, and wonder if I might know my own community better than an atheist. That just possibly might be the case, right? In the end, time will tell. Let me make my case, and let’s see what happens. Certainly let me know of any scientific errors you find. I need this to be above reproach. On what YECs will or won’t do, that is a different question. Let me make my case without having to guard my flank.