Nohi bus to Kamikochi during autumn festival

Hi,

We will be in Takayama for the Autumn festival this year, staying there 8th-11th October.

We were planning to see the daytime and evening festival on the 9th, then on the second day of the festival (10 Oct) we want to go to Kamikochi. Apparently you can't reserve the Nohi bus to Kamikochi via Hirayu online. I imagine it could be extremely busy with the festival crowds, so is it possible to book a specific bus in advance (e.g. When we arrive from Matsumoto on the 8th), or do we just have to chance it and hope the queue isn't too horrendous when we arrive in the morning?

Does anyone have any experience visiting Kamikochi while the Takayama festival is on?

Thanks very much!

Tom