Well, a reduction in the time it takes to remove the bad thing, is a positive, isn’t it?

I think what they means is that the amount removed per unit time remains the same, so if the body spends less time removing cortisol there will be a buildup.

this is hilarious. two comments from two different users made the same apparent mistakes with their intended meaning.

"reduces the time taken" = "speeds up"

From context, it seems like the intended meaning is that caffeine slows down the cortisol removal, but what was actually written was that it speeds up cortisol removal.