When is the earliest an npc can call you for a rematch in hgss?

Question

In heart gold, lass dana can call you for a rematch and if you do this you can get a thunderstone but when is the earliest this can happen?

Answer 1

Our memed pal, Youngster Joey!

Source

Comments

youngster joey is a meme?

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wait, how does this answer when npc's can call me back?

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They can call you at any time — onyl sometimes will they ask for rematch though.

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so its random?

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Basically.