1. Kushida is challenged by Ichika to a fight, not a challenge but Ichika makes it clear that she was going to punch Kushida.
2. Kushida is punched by Ichika. This is indicated when Kushida notes that her vision started getting distorted suddenly. (I will come back to this, but just remember that Kushida never clearly registered what happened with her but only felt her vision getting distorted, without there being any signs of anything else.
3. Kushida narrates that the sound of her cheek getting punched came later on.
4. Kushida tells the reader that before she knew "it", she was already looking up at the cloudy, overcast sky. This suggests that she was lying horizontally on the ground at that point. (Highlighted "it" for explanations)
Kushida said before she knew "it", now, there's a variety of possibilities of what this "it" means, but here, even if to lowball, we were to apply this to the sentence very ahead of it, it would mean that Kushida was already laying on the ground before that sound came.
Now,
the brain does link senses, a phenomenon called as linking of senses or senses integration, meaning that all your senses are added with a natural delay to have all your senses work as in real time. While I did give my own views on this and use a 5 ms addition of a timeframe, I do not actually think it is really necessary but it's cool, I guess.
That explains the "distortion" of vision which Kushida experienced as well, which mainly took place through her sudden changing of the FOV (from seeing horizontally to up ahead) which is normal and can occur very easily, but it is obviously not Kushida's eyes being covered with blood at that moment, no she wasn't dying already.
The thing here is that we already know this, and we are trying to make sense of how the delay arose. The opposition thinks that the delay arose because of delay in senses because Kushida was in a momentary daze (again, it is not mentioned anywhere, neither does Kushida happen to be in a daze in any time near and is even said to have active thinking in the feat itself). We are waiting for an anime adaptation for the same. The feat is already an FTE feat and would scale high enough for the current state of the verse already even through a lowball, we are just trying to make the best of the feat without rushing it, that's it. There are no textbook-level problems in the feat interpretation itself, mainly about how it happened.