Would like to recommend doing the individual server maintenance not at times which is for most players the preferred time to play the game like in America in the evening.

In my opinion it would be best to start maintenance in Asia when it is 2am in Korea, in Europe when it is 2am in Central Europe and same for America.

Also, it gives the players which are on more than one server less interruption of game time.

Additional you can reduce problems which might occur during maintenance on the other servers.