These two videos are a great resource for this subject:
Watch this video first:
https://youtu.be/Z0-6eUBBlg8
Then watch this video second:
https://youtu.be/-6ocRbEU7io
I prefer a different method than the 2nd video. I still prefer to cook my briskets to fully tender, then rest on the counter to IT reaches 145 and hold in the warmer at 140, but these videos above are a really good source to understand how you can react on the fly and determine if you need to adjust your rest time on the counter/IT temp when putting in oven/oven temp. Here's a few hypothetical scenarios to explain it better:
1) Pull it when 65% of the flat is probe tender, temping at 190 in the thickest part: I'll remove from the pit, no counter rest, wrap tightly in foil to trap in heat, and put directly into my warmer temp at 145. The brisket will take 6-8 hours to come down from 190 to 145 and that extra long time and carry over cooking at a very low temp will finish the brisket.
2)Pull it when 80% of the flat is probe tender, temping at 195 in the thickest part: I'll remove from the pit, wrap in foil, let it rest on the counter until IT is 170, and put into my warmer at 145. The brisket will take 4 hours to cool down from 170 to 145 allowing some carry over cooking to finish it.
3)*preferred method for me* Pull it when 90% of the flat is probe tender (don't mind if 10% is undercooked vs. overcooking 90% of it), rest on counter in bp until IT 145 (60-90 minutes), put in 140 warmer. Minimal carry over cooking with this method.