None stay onsen in Minakami

I have plan going to Minakami but I can't reserve onsen hotel. Please let me know where is reserve onsen 2-3 hr. in a day time.

Here is a summary of some of the best baths that are open to non-staying guests:
http://www.japan-guide.com/e/e7463.html

Or do you need a private bath? Note that they will be smaller, less attractive and rarely available for more than 45-60 minutes. I have no specific recommendation.

A few ryokan also offer daytime plans, but I am afraid I know of no specific plans, and most such information is in Japanese only:
https://tabihatsu.jp/special/onsen/minakami.html

Kashikiri onsen (time reserved private charter) is usuallu 30 min. to 50 min. max.
Most places offer day use so ask but only a few offer kashikiri and mostly indoor. Some offer a resting room with lunch package(not cheap).
http://www.kashikiri-onsen.com/