Apple Motion 4 - Manual (Page 557)

Trimming Keyframed Effects
When the duration of an effect such as a filter or behavior in the Timeline is changed,
keyframes applied to that object are scaled accordingly. This means that an effect
keyframed to change over time speeds up or slows down if the object it is applied to is
shortened or lengthened.
After
Before
Changing the duration of an object does not modify keyframes applied to attributes in
the Properties or Object tab in the Inspector. Keyframes appear in the area underneath
the object bar if you choose to show keyframes in the Timeline.
You can also speed up or slow down a keyframed effect by resizing the effect bar in the
Timeline.
557 Chapter 10 Keyframes and Curves