What time do you call brock for a rematch in heartgld?

To call Brock for a rematch in Pokémon HeartGold, you need to have defeated the Elite Four and become the Pokémon Champion. After this, you can return to Pewter City and challenge him again. The rematch is available at any time after you’ve beaten the Elite Four, so you can choose a time that suits your strategy and team readiness.