When is the best time to prune then spray and to thin the fruit on apple and peach trees.
Prune apples after leaves fall, peaches when they are growing, from late Feb until fall. Spray when needed. Spray is not just spray. There are pesticides and fungicides, you need to learn what your problem is before you select a spray. Thin apples anytime after blooms fall until the fruit is nickel sized. Peaches need thinned before the stone gets hard, otherwise you are wasting your time.
See you local county extension office (under USDA) for information for your county.