is that if you want a night time GV battle organize a group and create a custom arena to duke it out. Night time is part of the game, it's just enabled/disabled in the arena settings as I recall.
This is the best use of the custom arena - set up your favorite map with your favorite settings and get your friends in there. Even though the player limit is 16 in a custom arena, it's still great fun if you're all fighting each other instead of off sightseeing.
The setting for night enable/disable is not really there. You can set "dusk" and "dawn", meaning when the sun sets and rises, but the game jumps right from dusk to dawn without ever going into "night". If you set "dusk" for 22:00, the sun will set at 10pm and then jump to whatever time you set for "dawn".
You have to manually set the time somewhere between dusk and dawn to have it be night - "true" night is programmed for 05:30. Set your time for that with a timescale of 0 to lock it into night. But, it's kind of neat to start at 4am with a timescale of whatever you want so the game clock advances - eventually you'll see a nice sunrise as daylight breaks.