You can use the Meraki API to get the firmware status of all devices in your network. You’ll need to iterate over each device and check if it’s running the latest stable firmware. If a device is not running the latest stable firmware, you can schedule an upgrade.But, it's not possible schedule it directly, you need to use the Meraki API and cerate a python script for it.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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