The bus timetables (in Japanese) are available on the website of Zao Liza World.
During the season from the late April to the early November of 2018,
two buses are scheduled to go each way in a day.
This bus service is free of charge. http://www.zaoliza.co.jp/summer/access/2018ekoogou0427-1104.pdf
Departing at 09:20 / 13:25
from JR Kaminoyamaonsen Ekimae Koban Mae
(in front of the police box near the West Exit of the station),
arriving at 10:20 / 14:25
to Katta Parking Lot.
Departing at 11:15 / 15:30
from Katta Parking Lot,
arriving at 12:50 / 16:25
to JR Kaminoyamaonsen Ekimae Koban Mae.
From Katta you go up by lift for 7 to 8 minutes,
then walk a little to the site where you would have a view of the creator lake.
(Lift operation hours: from 09:00 to 16:30.)
The round-trip lift fare is 750 yen. http://www.zaoliza.co.jp/summer/kattarihuto/http/top.html
In October, the autumnal rain front and/or a typhoon may affect the weather in Japan.
I recommend you have a Plan B, and also pay attention to weather forecasts and related information.
- Japan Meteorological Agency
: One-week forecasts: Yamagata http://www.jma.go.jp/en/week/311.html
: Tropical Cyclone Information https://www.jma.go.jp/en/typh/
Enjoy your trips!