Cooking times: Cooking times will vary based on the apple used. Some apple varieties are juicer or firmer than others. Cooking times will also vary based on the crock pot size.
To check for doneness: Spoon out some of the apple butter, turn the spoon upside down. The apple butter should cling to the spoon without falling off right away. If it does fall off, continue cooking to remove more of the liquid. Alternatively, you can spoon a mound of apple butter on a plate and watch to see if liquid forms around it.