From Tokyo station get on Shinkansen ASAMA to Nagano city - 90min, 222km ¥8.000, 222km
In Nagano station change for Nagano Dentesu Line to Yudanaka st. in Yamanouchi town - 50min, 33km, ¥1.230 express, or ¥1.130 not express
From Yudanaka station - you can take public bus and get of at Kanbayashi bus stop, or take Taxi up there - 7 min, 7km, ¥1.500 (buy tickets from the bus booth just next to the train station)
From Kanbayashi follow the signs of Snow Monkeys and you have to walk 25min, 2km
•Your JR pass doesn't cover train from Nagano st. to Yudanaka st. -it's different train company
The bus at Yudanaka station is available every 30mins, so no worries.
I got worry because i estimate reaching yudanaka station probably around noon then walk up there, come down, maybe 3pm or 4pm liao? last bus picked from Kanbayashi is when lei? do you know the exact bus number or name?