I too have a few seedlings I grew from leftover apple cores, currently in pots, also approximately 8" tall. So long as you don't mangle the roots and keep them well-watered, you could plant them any time from now to October/early Nov.

You will want to get them in the ground before freeze-up; nature isn't kind to potted plants in our northern climate.

For rabbits and deer, the only thing you can really do is fence as securely as possible. What I do is use old tomato cages too beat-up for garden work as a scaffolding around which I wrap chicken wire.