I'm no professional at retiming nor have I tried to speedrun this game in any way, but I'm not confident to say that the retiming methods used for reaching water are correct. I've seen some (especially the world record) that were retimed using yt-frame-timer. I can 100% confirm that the time is not completely accurate. Another thing is that it would be easier to use math when retiming. By this, I mean subtracting the starting frame from the ending frame and then dividing that number by the framerate (of the game, not the video). I'm not familiar with the physics of this game, but I would make an assumption that the runners who walk directly forward into the water would all have the same time. If I am wrong about ANY of this or you would like to inform me about something that I am unsure of, please reply.

Professional Retimer here! My official way of retiming water runs is when the bubble particle shows up on screen. The issue with this is, people don't always look at the water when they drop in so most of the times it's a guessing game. Audio isn't much of a help either because some runs have it, some don't, some have delayed or glitched audio and YouTube or it's frame retimer doesn't have an audio visualizer. So usually I just judge based upon the angle at which they look at and how far they sink into the water. Hope this provides some insight.