Don't grow them but I found this...
"The time to harvest Oriental persimmons is normally signaled by the first frost. The fruit may be stored on the tree; however, they continue to ripen after they are picked. Picking a little early prevents loosing fruit to birds and other wildlife."
HTH

Here is a link that might be useful: More about OP

I'm sure your trees will do fine in the cold weather. I had a couple of young trees at my previous home, and I have seen huge old ones at a nursery in Huntsville, AL, which is colder than where you are located. One of my Japanese Persimmons was a nonastringent variety, and as I recall, it ripened before we had frost (and I was in a cold pocket that had early frosts).

I have one Oriental Persimmon in a pot that I need to plant this Fall. They are really beautiful trees - great bark, nice foliage, good Fall color. And the fruits are delicious -- much better than the wild American persimmons. They should be used much more than they are!