'In Pokémon Emerald and all subsequent games, Magma Armor halves the number of cycles it takes for a Pokémon Egg to hatch, provided that the Pokémon with Magma Armor and the egg are both in the party. All eggs that are in the party at the time are affected.
This effect will not stack up if multiple Pokémon with Magma Armor are in the party, nor will it stack up if a Pokémon with Flame Body, which also has a similar effect, is in the party.'
I dont think I need to paste this twice. It is basically the exact same for Flame Body.
So from Emerald on.