Deleting Frames: http://manual.reallusion.com/Cartoon_Animator_4/ENU/Pipeline/Content/Resources/ENU/09_Timeline/Deleting_Frames.htm
This will do what you're after. It will also shorten the project length by the same amount. However, if you're zoomed in on your timeline, this might not be apparent and might explain why you didn't think it had worked when you were trying it.
- Create a new blank project
- At t=0, add a small prop at one side of the screen
- Move the playhead to, say, t=10 seconds
- move the prop to the other side of the screen
You now have a simple animation that will take 10 seconds for the prop to move across the screen and stop at t=10 (or, if you prefer, keyframe 300).
Now use the steps from the link to delete project frames from the middle of your animation. Delete, say, about 150 frames (5 seconds) worth of the project.
Now play back and you'll see that it has indeed shortened your project. Hope this helps…