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Gravity travels at a finite speed, the speed of light. In a binary system the companion star did not appear out of nothing, the mass has been there for ever.
The equations in Wikipedia are for the 'instananeous' case. The equation must be summed over all pairs in the system; they give the answer at a particular D for a particular pair at a particular time.
To be more correct you could replace the D with a function containing T time.
As the bodies orbit each other the center of mass for a n body system will change at the speed of light.
Also you cant really check this because your communication of the measurement if you could actually make it would also be limited to the speed of light.
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