The length of a Clip is automatically adjusted to the overall length of the objects that are part of it. In other words, you don't have to change the length of the Clip yourself, it does that automatically.
As the following example shows, the Clip starts where the first object (in time) starts, and it ends where the last object (in time) ends:
If you want to shorten or crop the Clip, you have to change the duration or the timing of the underlying objects. In this example, you could either do this by:
The Clip length will then be adjusted accordingly.