Watched your video and just sat thinking about it a little bit. I'm going to type out loud.
This only happens with key switch in position II, lights. 
So, if the issue was with the stator plate, I would think it would manifest regardless of key position. I would test this by disconnecting the yellow wire from the stator harness to the main harness with the key in position II.
This of course has to change the issue, the engine should be OK. If not, there's a problem with the night time charging system circuit that takes over in key position II. G/R wire, checked by disconnecting from the stator harness to main harness.
To further vet the lighting, if it's lighting, I would move forward, and disconnect the blue wire from the ignition switch feeding the light switch.
If no change, I would plug the blue back in and disconnect all lights, and test again in position II.

This is what I would do if I was you. Results may vary and be completely inaccurate or worthless 

Apex; Thanks for the thoughts. I have completely eliminated the switch and the wire harness by connecting just the light directly to the yellow light wire coming out of the magneto. I put the switch in position 1 and tested and in position 2 and tested. It only shifts the timing when the light is drawing power from the light coil. disconnected it runs fine, connected it misses. (I should say it causes the timing to jump around as it does not actually "miss") Perhaps "stumbles" is a better word.