**Core Concept**
The closure of cleft lip involves a series of surgical techniques to repair the lip and achieve optimal aesthetic and functional outcomes. This procedure requires careful post-operative care to minimize complications and promote healing.

**Why the Correct Answer is Right**
After a cleft lip operation, all the stitches are typically removed on the 5th to 7th post-operative day. This timing allows for the removal of the sutures before the scar starts to tighten and form a noticeable line. Removing the stitches too early can lead to dehiscence, while waiting too long can result in a more noticeable scar. The optimal timing for suture removal is usually between 5-7 days post-operatively, allowing for adequate wound healing and minimizing the risk of complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Removing stitches on the 1st day post-operatively is too early, increasing the risk of wound dehiscence and infection.
**Option B:** Leaving stitches in for 10-14 days post-operatively can lead to a more noticeable scar and increase the risk of complications.
**Option C:** Removing stitches on the 3rd day post-operatively may be too early, as the wound may not have healed sufficiently.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the timing for suture removal may vary depending on the individual patient's condition and the surgeon's preference. However, in general, removing stitches on the 5th to 7th post-operative day is a widely accepted practice in cleft lip surgery.

**Correct Answer:** D.