Onsen (hot springs) in Japan typically open at 9:00 AM and close around 9:00 PM, with operating hours varying depending on the specific spring. Some may have earlier or later opening times, but generally, you can expect to visit an onsen between these hours.
Please note that some onsen might be closed during meal times (usually around lunchtime) for cleaning purposes.
It’s best to check the specific rules and regulations of the hot springs you plan to visit before going. Additionally, many onsen have strict no-outside-food policies or require guests to shower naked upon entry.