Onioshidashi Park

Hi.
Intend to visit Karuizawa area in early November for the autumn foliage.
How many hours does one recommend to spend at Onioshidashi Park ?
Also, are there any eating places in the area ?
Thank you.

I recommend 30-90 minutes without the time for a meal (there are recommended 30, 40 and 60 minute walking courses). There are a few food options inside the park:
https://www.princehotels.co.jp/amuse/onioshidashi/map/

Thank you Uji.
I ask because the bus timetable seems to dictate how much time we should spend at the park :(
arrive at the park at 10.45am and the next bus departing the park is only at 1.30pm !

Also, how much time should we allocate when visiting Shiraito Falls ?

Thanks in advance.

About 20 minutes. There are also some light food options there, which can prolong the stay by 5-15 minutes.

Thank you Uji.

A slightly unrelated question, it is forecasted to be raining on one of the days we are in Karuizawa (likely whole day).
Not the best time to be outdoors, but if we have to, which sight is slightly better for a rainy day :
- Onioshidashi Park
- Usui Pass observation
- Shiraito Falls
- Kumoba pond

Thank you in advance.

If visibility is limited - it often is on rainy days - then I would go for the sights that are not wide and open like the Onioshidashi Park and Usui Pass observation, but instead go for more compact sites like the Kumoba Pond and Shiraito Falls where you can appreciate the sights even when visibility is bad. If you visit by public transportation, I would be careful about bus connections to/from Shiraito Falls, because you don't want to hang around there too long in the rain. A main attraction of the Onioshidashi Park and Usui Pass observation deck are the vast views over the wide landscape, which cannot be appreciate when visibility is limited.

In case of rain I would go to the wonderful Hiroshi Senju museum in Karuizawa

Onioshidashi has a number of good photo spots. As you mentioned though, going by bus is not that convenient - there are only a few per day. So by all means learn the schedule, and make sure you don't end up stranded there or are killing hours of time waiting for the next bus.
https://youtu.be/It48UQXW4-E