I heard the March of Time happens when Rome (the EB faction) holds a Huge city in the Italian peninsula apart from Rome. So definately Capua, Ariminum, Arretium, Arpi and maybe Rhegion, Taras, Segesta or Bononia.

It kinda sucks if Roma gets wiped out of their homelands early in you campaign because when the march of time event strikes and you're playing Baktria you get Hetairoi Kataphractoi - the sexiest bodyguard unit in the game.