Use the linear regression to log you rng numbers and calculate the optimal final cart time.
Lol, I thought you were being facetious but then I saw your link to find that you're serious! Very nice guide. I don't plan on ever charm sniping again, but here is my data log for sniping my Sharpness+3 000 talisman:
Sharpness+3 000 2367
90s (Final Cart 48:30, first cart 49:29) 2269 2329 2279
The RN clock ticks faster in the secret area room, so I found that varying my first cart times changed the RN of the final talismans more than varying my Final Cart times in Area 1. My data log should express that consistency. However, I do believe it is best to establish an optimal Final Cart time, either via linear regression or just plain data sampling like what I do, but only after you have fixed your first cart time.