I'm not saying it applies in this case, but I was in radio about that time and most of the switches were made at "sundown" — i.e., about 5 or 6 p.m. in the winter and about 9 p.m. in the summer. My recollection is that different stations chose slightly different times, but the operative word in their licensing was "sundown." Not sure that's too helpful specifically for WWVA.

My recollection of the power agrees with Pete's — 50,000 watts, clear channel. You might contact the Federal Communications Commission; they should have records of that kind of thing, since they were the licensing agency.

cheers,

david