There isn't really a specific time to how fast your Pokemon level up. The younger the Pokemon(smaller the level) the faster they level up. also battles the Pokemon is in give it more experience. so if you wanted to level up a oddish and you gave it exp. share it would get less experience than if it was the first in the party/ battled the enemy Pokemon itself.
If you trade what you want to train to a friend and give the Pokemon a lucky egg it well level up really quickly, only a few hours to wait and it will be level 100 in no time.
you can't get the black flute in leaf green but you can in Pokemon ruby, sapphire and emerald then trade it to leaf green.
haunter has to be traded to evlove haunter evolve into gengar in level 42
go to mossdeep city then head left and go past the white rock at the end their should be a house with a fisherman in it and he will give it to you
latios and latias appear in random patches of grass and areas of water after you catch Rayquaza or make him faint.(after saving the world in Sootopolis.)
To get a Pokemon level up quickly is to have a Pokemon hold exp. Share and then just battle a bunch of trainers or wild Pokemon.
i beat that gym with pokemon in their high 20s but i had a full team at that point, ideally you want your pokmon to be mid level 30s.
Wynaut evolves at level 15 in Emerald.
Combusken evolves at level 36 in Pokemon Emerald.
Snorunt evolves at Level 42 in "Emerald."
Torchic evolves into Combusken at Level 16.In Emerald it is at Level 17.
Combusken Evolves Into Blaziken At Level 36 In Pokemon Emerald.
ABXY