[alexander_busek]

That appears to mean it is impossible for a measurement to be taken.

No, not "impossible."

Rather, the experimenters themselves impose this restriction - since, if the measurement were taken after a photon could theoretically traverse the distance, the measurement wouldn't prove "entanglement."

Only when the scientists can point and say, "See, the particles must be entangled, since the measurement was made before a photon could have traversed the distance separating the two particles!"

Regards,

[Fungi]

What they are measuring travels at the same speed as the measurement.