I know this isn't from seed, but the fastest way to start apple trees is to trim new growth from the branches of the desired tree. You want a piece about 5" to 8" inches long with a couple buds on it. Cut the end at a slight angle and using the edge of a knife lightly remove the outer layer of the young bark about an inch up from the bottom. Not down to the wood, just the young outer bark. set the end of the branch that you are going to plant in tap water for an hour, I've left them up to a day before.
Dip the damp end in rooting hormone, you can also you banana peels. tap off the excess rooting hormone and plant in potting soil. we used fine peat moss mixed with compost. keep the soil moist not wet. check for root growth in about a month. Roots should be at least a 1/4" long.
you can keep it inside all winter the first year as long as it warm and get lots of sunlight. We did hundreds of trees this way every year. we usually had about a 10% loss after the first year.
The link below is similar to how we did it.
Grow apple trees from a branch.