Quoted from trihedron:It's a special mode where extra points are awarded and un-usual / fun sounds, lights, etc are played at exactly midnight. Basically during a ball if the clock hits Midnight while the game is in play, the machine "turns off" and then shows "MIDNIGHT MADNESS". Then you get to play for a few minutes.
Here is a video I recorded in January of my Johnny Mnemonic's Midnight Madness:
» YouTube video
wow looks cool on Jm, is there a list of machines that does that?