Marvis Minis continuously validates the health of network services by performing synthetic tests at predefined intervals without requiring user intervention. These tests simulate real client interactions --- such as authentication, DHCP, DNS, and application reachability --- to detect network issues proactively.

According to the Juniper Mist Marvis Minis Technical Overview, the feature performs:

''Automated validations every hour to ensure wireless, wired, and WAN network services are operating as expected.''

Each validation cycle allows the Minis agent (running on Mist Access Points) to verify connectivity and performance parameters across key stages of the client experience. If any issues are detected, they are automatically surfaced in the Marvis Actions dashboard for further analysis.

While administrators can trigger additional manual tests, automatic validations occur every hour by default across all enabled sites.

Therefore, the correct answer is B. Every hour.

-- Juniper Mist Marvis Minis Operations and Validation Guide