Some react faster and some react more slowly, but the average driver's reaction time is one second.
Readiness for action, a defensive driving style and high risk awareness combined with a lot of experience are crucial for a good reaction ability.
It is your reaction time and the car's speed that determines how long the reaction distance will be in a braking event. The reaction distance is the distance the car travels from when you discover an obstacle or a hazard until you apply the brakes.