Here's what I have recorded:
A clip showing a flash appearing on screen at the 7 second mark as the other Hitokiri executes a Conqueror:
https://i.imgur.com/fM77nDG.mp4
And this one where 5 seconds in, you can see the flash appears exactly when the Hitokiri on the far right executes someone. The flash occurs again 19 seconds in after you can quickly see the Hitokiri starting up that execution at the 16-17 second mark in the background:
https://i.imgur.com/pHoe1TC.mp4