How long do Black Flute repel and White Flute attract effects last?
Solution 1:
Black Flute:
Reduces wild Pokémon encounter rate by 50%.
White Flute:
Increases wild Pokémon encounter rate by 50%.
According to Bulbapedia.
Regarding the duration, there's a controversy about their effects.
As different people on GameFaqs suggests here, here and here:
White and Black Flutes should only work for one step each time they are played.
However, on this forum is explained that:
The White Flute and Black Flutes raise and lower the encounter rate, respectively. They last as long as you're in the general area you used it.