It works by AND with magical heat removal and magical radiation removal.
I was referring more to this:
"specifically approximately 4 billion years worth in the first three days of Creation before there was any life to kill"
Life is hardly the only problem. Rocks will be changed by the massive production of heat as well.
Also, having two eras of extreme decay rates should produce rocks with one of two ages, either 4.5 billion years old or 500 million years old. There shouldn't be anything in between, and yet there is. Even if we grant magical heat removal there is still the problem of a whole range of dates that shouldn't be there.
It supposedly isn't producing radioactive elements. They think that 40K was around before the Fludde but somehow living things had isotope sieves that prevented them from incorporating it into their bodies.
There is carbon isotope fractionation in photosynthesis, but it is only about a 1% shift towards one isotope, hardly the all or none needed in this scenario. If you are going to have naturally occuring biochemistry do this fractionation then it begs the question of how it was lost across all life. Surely we should find some remnant of it in modern organisms.
It reminds me of a time when I was having a discussion with a creationist on the topic of inverted retinas. He made the assertion that perhaps the human retina faced forward, but then became inverted after the "Fall". I then pointed out that ALL vertebrates have an inverted retina, and that his scenario would require the retinas to invert in thousands and thousands of species over the span of just a few thousand years. It just isn't practical. I see the same problem with isotope fractionation.