I went back and watched my video (as well as other karters) multiple times and had a really hard time finding any brake markers. I guess there are three 6″x6″ squares starting about 300 feet from the apex of the cones. But if you started braking there you would have no chance of making the corner.
Like Robert mentioned the white line running across the track that is probably 500 plus yard out of the apex is when you need to start braking (at least in a F125). But that is when you have to start braking since you are going from over 100mph down to about 20mph. So if MKC is adding bigger brake markers make sure you go all the way out to that white line.