Early Bird (ability)

In battle
Early Bird causes quick awakening from sleep. In the turn the Pokémon is put to sleep, the number of turns it will remain asleep is preset. If it is 6 turns, it will be halved to 3. If 3, it will be rounded to 1. If only 1 turn is preset, it is rounded to 0, causing the Pokémon to instantly wake up at the end of the same turn. This also applies to the self-induced sleep from, reducing its length from 3 to 1 turn.

Outside of battle
Early Bird has no effect outside of battle.

Trivia

 * Early Bird is the signature ability of Cheepip and Aeroma, although this doesn't seem to be intentional.