The Motion Blur node has a Speed and Timing curve, similar to the ones in the Timewarp module. Use these curves to modify timing over a sequence of frames to add complex effects to a clip.
The Speed curve and Timing curve are dependent on each other. You cannot change the speed without affecting the timing. When you move a keyframe on one curve, the other curve moves as well. Enter a value in the TW field to specify the timewarp as a percentage of the source clip.
To use the Speed and Timing curves: