Instructions
Take your egg to one of your Digimon farms and place it in the field.
Travel to the Farm Goods Store in the Shine W area.
Purchase as many items as you can that raise your egg's defense and dark XP.
Return to your farm and feed said items to your egg. Chaos Eggs will be ready to hatch once their defense level reaches 230 or more, and their dark XP reaches 5,000 or more.
Talk to the egg once its defense and dark XP have reached the appropriate levels. It will hatch automatically.