WIll it take longer (and if so how much longer) to cook 27 pieces of chicken rather than 3?

It might take a little bit longer, because you will need to fit two pans into the oven to hold that many pieces, and you will have more moisture in the oven from the meat. I would think it would not take more than 5–7 minutes more. You may want to swap the bottom and top pans around half way through the cooking.

If they all receive the same amount of heat for the same amount of time, they will be equally done. If your oven struggles, or if it heats unevenly from rack to rack, or if you block the air circulation with big trays you will get uneven results.

The size of the individual 27 pieces is not any denser than 3 individual pieces, so the heat will have the same distance to go through in order to cook the meat. Unlike the difference between cooking a big turkey vs. a little turkey, where the mass of the meat is different. The only thing changes is how much heat is actually in the oven because of moisture, radiation from the heat element, and as @pdworkin said, the air circulation in the oven.

If I were doing it, I would do each pan, however many, separately. I would much rather do that than play guessing game with multiple pans and uneven cooking.

much like I’d rather drive a longer distance just to not sit in traffic.

use a meat thermometer, and check each piece individually. Of course, many cooks can tell if a piece of chicken is done by how easily a fork goes through it.

I wonder if there’s a way to test it like the cheater method for testing steak? (Poke your chin, that’s rare. Poke the tip of your nose, that’s medium. Poke your forehead, that’s well done)

@poofandmook yeah, if a fork goes in easily and comes back out easily, and the juices run clear, the chicken is done.

@Psychedelic_Zebra: Well, yes, but I meant without stabbing it and letting all the yummy juices escape :)

It was all good… I used ALL your advice xxx as usual