I think 28/7 was an important date, it's introduced in 5DAS and in 6DAS it's, like other things, given a new mystical meaning.
My guess is that "It hurts" is related to Chzo's being an "elemental of pain". But according to what I remember either it happens following the script, or totally at random regardless of the actions you try.
Yes apparently we are really supposed to believe that EVERYTHING that happens in the ENTIRE series, is simply leading up to Cabadath's replacement by Dacabe/DeFoe, otherwise I'm missing something too... Also the whole story looks completely deterministic and like DaCabe couldn't do a thing to resist Chzo's plans, which are accomplished exactly the whole time. However I myself don't like this instalment as much as the others.