**Core Concept**
The question tests the understanding of lactation physiology, specifically the timing of peak breast milk production. Lactation is influenced by hormonal changes, particularly the decrease in **prolactin** inhibitors and the increase in **prolactin** itself after childbirth.

**Why the Correct Answer is Right**
The correct answer is related to the natural fluctuations in milk production that occur as the body adjusts to the demands of the newborn. Typically, breast milk production increases over the first few days postpartum and reaches its maximum around 5-7 days after birth, as the **colostrum** transitions to mature milk. This is due to the establishment of a regular feeding schedule and the body's response to the frequent removal of milk from the breast, which stimulates **prolactin** release.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it's too early for peak milk production.
**Option B:** Incorrect as it doesn't align with the typical lactation curve.
**Option D:** Incorrect because milk production usually doesn't peak this late.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that frequent breastfeeding or expression of milk in the early days helps establish a good milk supply. Understanding the normal progression of lactation can help in identifying issues such as low milk supply.

**Correct Answer:** D. 5-7 days.