The “less-than-one percent” variation was not repeatable in the controlled experiment, per the article, however.
I'm giving the creationists the benefit of the doubt on that one. Even if it were true, and even if solar activity and flares were far greater on the ancient earth, and I'll even given them a TEN percent variance in radioactive decay (or well over an order of magnitude of what was allegedly observed), then what does that shave off? 450,000 million years. Let's make it 50 percent. That makes the Earth 2.5 billion years old. Ninety percent? We still have the Cambrian at 450 million years.
In other words, the level of change in radiometric decay would have to be astronomically more rapid to even begin to move the age of the Earth to the same zip code as 6,000 years.