How long should I cook apples in the oven?
Various factors influence the consistency of an apple when it bakes.


Acidity. The more acidic the apple is, the better will the apple preserve its pectin and remain its crunch. Also any acidic fluids surrounding the apple will make an impact here.
Thickness of the slices. Thin slices will make the apple heat up faster.
The surrounding environments ability to transfer heat. If the apples are surrounded by a watery liquid heat will be transferred much more quickly to the apple than if it was surrounded by air. Other kinds of liquids will transfer heat quicker or slower.


So you see there are no hard and fast answers. But knowledge of these factors might help you build up experience to make a qualified guess in each case.