To your question, the caramel only touches the inside of the cored apple. The puff
started about 15 minutes. At 20, it was mostly puffy but still pale.
Perhaps if I added the caramel at the beginning, its heat might have cooked the interior of the apple faster, but I don't think so. The first attempt was cooked for the same amount of time and it was only as soft as this one.
Peace of mind (not having the caramel burn) won over for me.
Also, the Dufour instructions say NOT to underbake the pastry. To quote them, If it collapsed when you take it out, it was underbaked.
Well, duh.
That's covering your legal butt with pastry dough.