All the transmitters would need to be shut down while people are climbing around the antennas at the top. It looks like a UHF TV station transmit antenna up atop that tower, and stations on UHF run something like 1/3 of a megawatt of RF. You don't want to be near that antenna if it's pumping out power like that. That means that the TV station has to go off the air, which means that they don't earn money during that time playing commercials. So you might as well change out all the lamps, and it's probably done early Sunday morning when most every viewer is sleeping in.
