I am trying to animate some limit distance constraints to give me a smooth motion effect of a tool closing, however, when I set the distance at the time I would like the tool to be closed (e.g. 60mm at 0 secs to 0mm at 4 secs), it doesn't move smoothly it just suddenly closes at that time instead of closing gradually.

Is there a way to make it animate smoothly and not just jump to the distance?