How to animate the "Copy location" constraint visibility?
Another way to do it is to animate the influence. If you want a sudden effect, then poor's way gives the desired result. However, if you would like to have a smoother effect, you could animate the influence factor.
Scroll to another frame, and and insert another keyframe set to 1
And then, go once again to the following frame, and set the influence to 1, and insert a keyframe.