i am not an expert but i have tried to cold stratify many times with mixed success . when the roots begin to sprout the plant is vulnerable to damage and should be carefully planted in soil.after that keeping it cold may slow its growth so as to delay it till you can safely raise it outdoors. if leaves appear it must have sun. the trick to all this is timing so your seed sprouts when it is time to place it where it will grow. so much depends on the type of plant and the zone and what you plan to do with the plant.i would plant this apple in a small pot and keep it cold till leaves appear thenkeep it in the sunnyest window till you r last hard freeze has pased apple leaves can probably survive a lite frost .you might not know that while many fruits will grow true to the parent plant apple seeds are notorious for growing into different kinds of apples than what they came from

You should plant the seed with roots in potting soil right away. If the root is stuck in the paper, do not try and free it, you will just break it off. Plant the seed with a little bit of the paper attached. Actually if you plant fresh seed out of the apple stratifying is not a requirement and you can go ahead and plant the other seeds as well. For good reason most of us do not plant seeds to grow a fruiting apple tree as it will take up to 10 years to find if the fruit is worth eating, and the odds are against it. If you want a apple rootstock to grow a standard size apple tree and plan on grafting a good eating apple on to it, that will work. Al