I was just thinking of doing this last week, but ended up following a traditional muffin recipe instead. It is fresh in my memory, though...

Most standard-sized muffins I've baked are done in 15-25 minutes. King Arthur Flour, in their baking cookbook, recommends increasing the oven temp to 425, then baking for 18-22 minutes, until puffed, set on the top, and a tester comes out clean.

They also state that a typical quick bread recipe, using 1 1/2-2 cups of flour will fill about 12 standard-sized muffin cups to nearly full.

I'd lower the cooking time only. The recipe should be fine as is. I'd start checking 15 minutes, at least, before your base recipe "done" time, and then keep checking. Also, use your nose.....you can smell when baked goods are getting close to done.

My favorite banana bread is actually a very old coffee cake recipe from the Better Homes and Gardens red plaid cookbook. It is supposed to be baked in an 8" square pan, but I bake it in a loaf pan half the time and turn it into muffins the other half. With the loaf pan, I bake it at 350 degrees F for about 40 minutes; I bake the muffins in paper-lined cupcake tins at 375 degrees F for 15-20 minutes. The extra heat gives the sugars time to caramelize, giving the muffins a bit more color that they wouldn't normally receive with the shorter cooking at a lower temp.

My baking time for muffins from a quick bread recipe is generally around 20min when the oven is 350F. Just keep an eye on them and try the toothpick, like melissav suggests.

I've done the bread to muffin switch and I agree with melissav completely. The cooking time is definitely less!

You don't need to adjust the recipe..just the cooking time. Just dish the batter into the muffin tins and just keep a close eye on the first batch to see how long it takes for them to be done using the toothpick test.

The baking time will most likely be less. I would check it halfway through the original cooking time and probably every 3-5 minutes thereafter by inserting a toothpick into the middle of a muffin. I don't think you will need to adjust the actual recipe, just the cooking time. Good luck!