I think it is percent of video watched, because if you check out the analytics in YouTube Studio, it says how many people are still watching by a certain point.

I think it is percent of video watched, because if you check out the analytics in YouTube Studio, it says how many people are still watching by a certain point. So your hack makes sense, but I'm not sure it would work because it is VERY hard to keep anyone's attention on YouTube. The moment it's something even slightly less than interesting, the vast majority of people go onto the next video.