In Pokémon X and Y, nighttime is considered to be from 9:00PM–3:59AM. [1] X Research source

If you don’t want to use Amaura in this battle for any reason, while your Amaura must be in your party, if your EXP share is turned on, then the Amaura will still gain EXP.

Avoid pressing the B button at all during the animation, or the evolution will stop.