Tom and Max have both hit it.
No two briskets are the same. The flat and the point may cook a different rates. They will each reach temps at thier own pace.
Did 11 flats for work last week, and they varied 1 hour and 20 minutes on finishing up.
And did 30 packers three weeks ago and they ranged 2 hours.
Like they say, they are done when they are done. Oh yeh, practice makes perfect.
RandyE