I want to get a shiny beldum. How can I change the time in my DS for change the swarms? I change to 23:59 and after 1 minute it didn't change the swarm, always saying Route 208 Dunsparce!
The species of an outbreaks seems to be determined using a formula, because it is not chosen randomly when the player starts the game that day. It is also possible that the species is determined the day before, though there is no additional evidence to support this. If the DS clock is changed or a different DS is used, then the game will detect this and will not change the species swarming until 12:00 AM.
Let the DS clock turn naturally, the game can detect changes in the clock. These means you can only get one swarm per day, so just be patient.
http://bulbapedia.bulbagarden.net/wiki/Swarms