Help with new Chojubai quince.

I just bought a very young chojubai from a nursery. I would like to know when I do the prune or cut back how big should I let it get first? And how far should I cut it back? As in the very first cut back.

Picture? Location?

I would let it get just big enough before cut back. And then cut back exactly the right amount!

I can post a picture soon. But I live in northern Illinois. Right not the tree is very then like 1.5mm thing to long trunks just over a foot long on both.