Like Smokin' says"that is the experience thing"
Sometimes gettin' it can be an expensive
process.
Seems like the original question was timing on the cooker,not when the packer is at its best.
We often have cooked butts/packers together,but time on the cooker will still vary.
If you have the feel on your stickburner,hopefully it is just a question of watching the clock on your FE and duplicating approx times.
I'm certainly not expert enough to pick the ,exact number on a brisket.
I'm also not smart enough to operate a brisket button for comps.
You cook a little smaller than we like,so times can vary.
Most folks find there is a wide variation in quality of choice briskets,thus the time variation.
When we cook comparable product each time,we practice pushing the temp edge,and have a little more confidence at comps in our clock timing.
Also,like Smokin' says,some folks take them to higher temps,until they feel done enough.
Also,will add to your time.
How much it continues cooking ,over long holding times,versus taking it off the pit shortly before slicing varies the time.
Folks that cook two,or even three packers may pull them off at different doneness levels and choose their turnin ,when they slice them all.
Like Scotty say,time is for planning,temps are for estimating readiness.
