It depends on the predicted date of delivery.
If the predicted date of delivery is far away from the ordering date due to the constraints in supplies, then the actual delivery can be much earlier. For example, while the predicted date of delivery is Dec 10-Dec 23, the actual delivery occurs on Dec 1.
If the predicted date of delivery is the next day, then the actual delivery will be on time.
Very seldom (never happened to me), the actual delivery is later than the latest predicted date of delivery. If the actual delivery is behind the latest predicted date of delivery, you can ask for a compensation from Apple and they will give you an electronic coupon.