When do Pokemon outbreaks change routes?
From the Discussion page of Pokemon Outbreaks (in regards to how to reset the swarm):
Actually, any sort of reset will work, provided you have not already saved on that date. I've taken advantage of this multiple times. If you save after the date changes, though, even if you haven't yet inspected a board, the swarming Pokémon will be set in stone. --AndyPKMN (talk) 14:16, 7 May 2011 (UTC)
Pokemon outbreaks are set by the date, lasting that whole date only after the swarm for that day has been set and saved to the cart.