motion blur options in the render settings windows?

[excentriPMNA2]

when Motion blur Position in the Render Settings is set on Start on Frame and Keys set to 3, and current frame is frame 5 , and Length is 1.0, what happens?
the following description is my idea.
The motion blurs in frame 5, and frame 5.5, and frame 6 calculate, therefore the composite motion blur result adds to the rendering of frame 5.

My idea is right, or wrong?

If the motion blur position is Center on Frame and Length is 0.5, and current frame is frame 5, and Keys is 5, the motion blurs in frame 4.75, frame 4.85, frame 5.55, frame 5.65, and frame 5.75, therefore the composite motion blur result add to the rendering of frame 5.

Is my idea right or wrong?

[lee_griggs]

Information about Shutter Controls can be found here.