Servo speed in a Toggle Code
Normal servos have a speed. It's their speed, and you can't change it. You can make it appear slower by moving in small increments, but you can't actually change the speed it moves.

With constant rotation servos the "angle" dictates the rotation speed, but even with those there is nothing you can do to change the relationship between "angle" and rotational speed.

Other than buying a different servo with a different degrees-per-second rating.