Tune into prof oak/Mary channel, they'll mention the swarm pokemon and where. If it isn't the one you want save, turn off and set your ds clock to 11:59pm, load the game b4 midnight and wait for the date to roll over, tune in again and see what the new swarm pokemon is. Regardless of whether it's the one you want or not save, if it is then abuse like normal from that point on, if not then redo the time to 11:59 again and proceed to check the new swarm pokemon.
The key is to reserve after each new swarm otherwise it won't change.
The key is to reserve after each new swarm otherwise it won't change.