Imagine two parallel conducting plates set at a distance of several meters. If one charges the two plates simultaneously then one would expect a small delay before they started repelling each other due to the time it takes changes in the static field to propagate from one plate to the other. Could one experimentally measure such a delay? I guess it would be so small and the deflection of the plates would be so weak that the effect would be unmeasureable. I don't know if one could use electronic field detectors rather than rely on the mechanical deflection of the plates.