[Closed] XRef Visibility

Is there a way to key frame the visibility of an XRef so that as one runs through an animation then on specific frames different XRefs hide, and other XRefs become visible? It is for a script that is designed to give the impression of a city growing…

The XRef.hidden property seems to correspond to the visibility in the in the dialogue, and oens not seem to be animatable? Is there a way around this?

Cheers guys,

Rich