Mesen 0.9.8 - 476 frames. Beginning is start button input to start the game (frame before it turns black.) End is first frame where the Checkmate box is being rendered, I noticed other people using this timing as well so I went with it. If it should be the first frame you can read "black is checkmated" then add 3 frames for 7.983

I will gladly explain how this run worked if asked!

Mod note: 307 frames, somewest claims the video runs in 61 fps, so might come back and adjust again.