Server maintenance is always announced in Kingdom chats and via both Facebook Community page and the official website Community at least half an hour prior to its start.
We do our best to keep the server downtime as short as possible. However, significant updates and major issue fixes may take more time than usual. Once the game is up, the maintenance post will disappear from the Community page and you'll be able to enter the game as usual.
Also note that every player in the game is offline during server maintenance, so no one can gain any advantage in any game event or tournament. You may want to visit our Community page to participate in a Community event while maintenance is in progress!