Timer balls are hard to come by in Pokémon Brilliant Diamond and Shining Pearl, especially at the beginning of the game, but as you reach the latter half of the game, they’re far easier to get.
You’ll find these special Pokéballs in the sleepy Celestic Town, where an ancient Sinnoh shrine resides. When you arrive, you’ll see that there isn’t a Pokémart. Instead, there’s an independent operation on the top left of the town. It’s like visiting one of those small neighborhoods in the middle of nowhere in the United States or Canada without any big brands to speak of.
As it’s far off the beaten path, you’ll need the defog hidden move, in addition to Cynthia’s potion to clear out the Psyduck blockade to get to Route 210.
The shop can be found near a green-haired woman and a small pond. It’s exactly in the upper left corner of the community. There’s no signage, nothing to indicate there’s actually a store there. Go inside and you’ll see two elderly cashiers. Talk to the man on the left. He’ll offer you Dusk Balls, Quick Balls, and Timer Balls for 1,000 Pokédollars each.
When you get a Timer Ball, they’re best used when the battle has lasted for a long period of time because their effectiveness increases as each turn passes. If you’ve used a Master Ball and cleared out the Ultra Balls, the Timer Ball might be your best option if you’ve kept a legendary Pokémon like Lugia at bay.
