New crockpot cook times rule?
There's no right answer to this, every brand is different. Plus, you are assuming that you will have this problem when you don't know if the pot you bought is hotter than normal. In any case as long as you have enough liquid in it and use a low setting you shouldn't have to worry about anything burning. 

My advice is to try a standard slow-cooker recipe and see how you do. If it cooks too fast then try bigger chunks.