Your reaction time doesn't come into play when calculating your ET. If that was the case, your ET would be based on when the light went green and when you crossed the finishing line. If the light went green, and you sat there motionless for an hour, then decided to take off, your ET is still going to be the amount of time it took to traverse the 1/4 mile starting from the time your car broke the beams at the starting line to the time it broke the beams at the finishing line.
