Thanks for checking. Yes, after the initial 5 minutes at 425°F, mine take another 10–12 minutes at 350°F. Oven temperatures vary quite a bit, which is why I also include the internal temperature in the instructions. The muffins should reach 195–200°F in the center before coming out of the oven, so if yours are still underbaked at 12 minutes, I would continue baking them at 350°F until they reach that temperature. I’d also be curious whether you baked a standard 12-muffin batch or made larger muffins, since that would affect the baking time.