Is there a criteria to determine whether I should perform Day 4, or even Days 8 and 12

....if the color does not change for at least 8 hours for Day 1, should I go on to day 4 at all?

...If the color does not change after 8 hours for any day; shouldn't I add the hydrogen peroxide to stop the process and then turn on the filtration system ?

Yes you should do day four and eight because even though "Treatment One" lasted plenty long enough, it didn't kill Fluke eggs or embryos. These have to be interecepted on those subsequent days.

After a potassium permanganate treatment of six to eight hours on Day One - if it hasn't converted from purple to amber, you can inactivate with peroxide, and probably should.