If there are no other apples around, then the seedlings may be selfed McIntosh trees which may or may not be good. However, apples normally require cross pollination so it may be that bees brought pollen in from another tree. So you may or may not have a good apple. The adaptability of nut trees will be dictated by the minimum temperatures in your area. At lower temperatures most of the Persian walnuts, European filberts, some heart-nuts and Japanese chestnuts may experience serious injury.
Harvest time varies with individual tastes and locality.
One may consider a fruit ripe while another individual believes it is immature. However, fruit picked too soon does not store well and does not develop full flavor. Also the background color changes from green to yellow. Generally speaking, as red apples reach picking maturity the green peel becomes slightly yellowish. Green or yellow varieties change from green to creamy white or yellowish as they reach maturity.