We have 23 APs on 3 floors.
We are wondering if we click Upgrade Now, how long would the upgrade take?
It will depend on the network on how long the AP takes to download the firmware afterwhich reboot.
Is wireless unavailable during the upgrade?
Wireless for the AP which is rebooting will not be able to serve clients
What is the impact on end users?
Lesser serviceable access point usage for users.
With a physical controller on AOS 8, I believe you will be able to allow live upgrade with no impact on operational network.
E.g access points with no clients will upgrade.
Or alternatively, I believe you will be able to see the usage of users to access points, you may like to consider to manually upgrade access points which are not serving any clients, considering that airwave and a mobility controller is not available.