Custom Motion file in Final Cut Pro X speed

I designed a custom 30 second animation file in Motion which is designed to be keyed over a changable background image in FCPX. It's basically a bunch of rectangles moving up and down and a constant speed and on the left side of the screen. I want this to be the top layer in Final Cut. Depending on how long I need to use this for be it 5 seconds, 20 seconds, or the full 30 seconds I want the speed of the animation to remain constant. But when I shorten the file in my Final Cut timeline the animation speeds up to reach the end of the the 30 second file. I just want to be able to use a portion of the animation and not see the full 30 seconds of it. Not sure how to accomplish this. Please help! Thank you!