I mean, from the release of the pitch until it gets to the plate, a 95-mile-an-hour fastball is around 425-450 milliseconds. On the other hand, it takes 150 milliseconds on average for a Major League Baseball player to get their bat around. So if you were to time how long it took for your fastest ball to reach the plate, it would be about 1.25 times as long as an average ball game.
Here's how long it takes for various speeds of balls to travel 10 meters: 400 milliseconds at 90 miles per hour; 450 milliseconds at 100 miles per hour; 500 milliseconds at 110 miles per hour; 560 milliseconds at 120 miles per hour; 640 milliseconds at 130 miles per hour; 700 milliseconds at 140 miles per hour; 800 milliseconds at 150 miles per hour; 920 milliseconds at 160 miles per hour; 1000 milliseconds at 170 miles per hour.
So a fast ball that reaches the plate in around 1 second would be traveling around 175 miles per hour, which is very fast by baseball standards.
The speed limit on most major sports fields is 40 miles per hour, so anything faster than that is legal. Pitchers can go even faster when they're working with a black ink pen, which is why their pitches appear to come out of nowhere. However, such speeds are dangerous and could cause serious injury to players who aren't used to them.
A fastball traveling at 90 mph may reach home plate in 400 milliseconds, or four-tenths of a second. A hitter, on the other hand, has only a quarter-second to recognize the pitch, determine whether to swing, and begin the process. The more time a hitter takes to react to a pitch, the easier it is for the pitcher to figure out what type of move he's making and change his approach.
Hitting is a very complex activity that involves skill sets such as batting eye-ball, footwork, hand-eye coordination, and mental preparation. Even though science has come a long way since its beginnings, psychology still plays an important role in baseball. Studies show that faster pitchers tend to get hit more often because they use up their pitches faster, which makes them more likely to walk someone.
As far as how much time you have to react to a fast ball, that depends on how well you can perceive movement and read bats. Most hitters can tell when a pitcher is working in the zone with heat versus breaking balls outside. This allows them to prepare themselves accordingly. Hitter's also need time to think about where they're going to hit the ball after seeing it leave the pitcher's hand.
Overall, you have around a quarter-second to decide how to react to a fast ball, regardless of how strong or weak it is.
A fastball traveling at 100 mph takes less than 400 milliseconds to reach home plate. The swing itself lasts around 150 milliseconds. Despite their popularity, 100-mph fastballs are still uncommon—rare enough that you won't see them in batting practice on a daily basis.
The fastest pitch thrown by any major league player has been 108 mph, set by Tampa Bay's J.D. Martinez on April 22, 2015. He threw the ball from a four-point stance, using only his arm and not his shoulder. The ball traveled 1 foot 11 inches into home plate for a strikeout against Atlanta's Jason Motte.
So yes, it is possible to hit a 100-mph fastball. But it's rare that someone will have an opportunity to do so in an actual game situation.