A Pokémon with Flame Body will cut egg hatching time in half, so the eggs will hatch 2x quicker.
The Hatching O-Power gives boosts based on the level of the power.
Adding Hatching Power Lvl. 1 will hatch the egg an additional 1.25xquicker.
Adding Hatching Power Lvl. 2 will hatch the egg an additional 1.5x quicker.
Adding Hatching Power Lvl.3 will hatch the egg an additional 2x quicker.