Ok. They will be stopped when you set them to somewhere around 90 degrees. Settings higher or lower than the stop position will make them rotate in one direction or the other.
To make your robot rotate 45 degrees, assuming differential drive, you'll need to start the servos in opposite directions, and stop them after the robot has rotated as far as you want. If you have no wheel encoders, or any other way of getting rotational feedback, you'll have to experiment with the amount of time to run the servos.