Hi Les,
I believe that would be correct. Basically, you are moving the timer to the sign end, therefore, you would then have continuous power from the buildin g to the sign. The timer would still be able to function to switch the sign on and off just as before.
You now have continuous power to run the 2 cameras, and you now have a mean s to transmit the signal over the gigabit power-line adapters. If the sign is using 220V, then you would only use one of the 110v leg and the ground/r eturn wire as a circuit for your cameras/POE.
Depending on what electronics that are being used for the sign, there is a possibility that some interference may be present. But, I would not keep th at from preventing me to proceed. That can be dealt with easily later if it rears its head.
Sorry for not responding faster to your thread, but Sundays is when I gener ally have more time for the forum. I am always extremely busy and it is har d for me to find time to relax and do what I want to do.
Have a safe and great day, and run like the wind with your brilliant epipha ny.