There are two kinds of reboot. Scheduled maintenance, and game updates. In both cases, there is a warning 30 minutes before the reboot, after which point brigands no longer spawn. There are further warnings at 20 minutes, 15 minutes, 10 minutes, 5 minutes and 2 minutes until reboot time.
Periodically, the server is rebooted. This only affects the ocean for that server, and the ocean is usually unavailable for a couple of minutes at the most. These reboots are timed to happen at 4am server time, but do not happen everyday. The text warning for a maintenance reboot is always as follows: "The server will be rebooted in XX minutes. This is a regularly scheduled maintenance reboot and the server will only be unavailable for a minute or two."
The server is taken down while the game update is released onto the server. This can take seconds or minutes, depending on the complexity of the update. The text warning for a game update is generally written by the developer taking the server down.
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