@Mike C, I think you're picking up on the right stuff there. There has been a lot of forum discussions on this subject in older posts but not as much here recently.
I think of it like a "top down" approach. Let's say today you could do 10x10 swings with 20kg in 5 minutes, but you struggle with 24kg... you can do 10x10, but only if you take 8-15 minutes total for swings. Should you train diligently with the one you can "test" with every day, 20kg? No. That would be a "bottom up" approach and would not drive progress as well as challenging yourself with a heavier weight. So you should train with 24kg, making each set as powerful and explosive as it can be, taking as much rest as you need to make sure that happens. Eventually you won't need as much rest, or stated another way, with a big push you could get it done in 5 minutes. Then it's time to start working in the 28 or 32kg.
So another way to think of it is that the goal (for your own physical results) is to competently and powerfully swing a heavier kettlebell in meaningful volume. The 5 min time standard for 10x10 are just an indicator of to what degree a given kettlebell has become almost easy for you, so that you can continue to train with a heavier one. Stated in this way, the 5 min isn't really the goal.
That's just sort of the way I've come to think of it. Hope that helps.