In College, in the pros it is a dead ball as soon as the ball hits the ground on an extra point.
Not anymore, the NFL moved the PAT back to the 15 yard line in 2016 I think and allowed it to be run back for 2 points if it’s blocked, that’s why the Cardinals elected to take a knee....
The NFL also requires teams to attempt a PAT even with no time on the clock because totals points and point differential are tie breakers in determining who makes the playoffs, etc..
They changed that rule. NFL to lengthen extra point attempts, allow defense to score on two-point plays