Hi Dennis,
Compost is a low and slow fertalizer, that it will encourage some growth; however, your concerns of new growth not hardening off, depends
alot on the climate you live in, and the health of the tree before fertilizing. Mellow climates with slow transitions into winter, provide adequate time for a healthy tree to transition to winter. Climates that can quickly and drastically change, or unusual cold snaps coming early can be the problem. If a tree is nutrient deficient, then late in the season its suddenly given lots of fertalizer, depending on its genetics, it may risk late season growth, rather then let those nutrients leach away.
The type of tree, your climate, unusual weather, the trees unique genetics, the trees health, and many other factors, can play into the tree properly hardening of new growth. Compost at any stage shouldn't be an issue, but for trees prone to the concern, hold off late summer early fall compost applications till after leaf drop. We're in early summer in the norther hemisphere, so compost away!