Once every 4-5 days is normal for a hatchling, so today or tomorrow would be fine.
If the pinkie isn't eaten, throw it away. Refreezing brings a risk of the food item going bad and causing a health problem if it's eaten when next defrosted.
If you want to be sure (or as sure as you can) that you don't waste food, feed tomorrow to make sure that your snake's appetite is keen.