How do I make an object begin following a path, but only after a certain point? I need to animate a ball moving up and through the inside of a robot. I have a path that is a child of the robot object, so it moves with the robot. The idea is that the robot will move up to where a ball is, then once it gets there, the ball can move on the path, and stop a certain point, then the robot will go back away and the ball will maintain it's new global position.

The ball needs to start on the ground, the robot (which has the path as a child) moves to the ball, the ball then follows the path for a little ways, then stops. The robot then backs away, but the ball needs to maintain the position it had before the robot backed away. 

I need to be able to turn off the influence the path has on the ball object at certain times, and turn it on at others. How do I do this?
If you use Follow Path object constraint(Ctrl+p -> Path constraint with object and path selected path being last/active), you have a property of Influence that you can animate(set keyframes to with i while hovering mouse over it) in order for it to start having influence only at some point.