**Core Concept**
Secondary haemorrhage after tonsillectomy is a serious complication that can occur due to various factors, including surgical technique, patient factors, and post-operative care. It is defined as bleeding that occurs more than 24 hours after the initial surgery.

**Why the Correct Answer is Right**
Secondary haemorrhage typically occurs between 5-10 post-operative days due to the sloughing of the fibrin clot that forms on the tonsillar bed after surgery. This process is facilitated by the presence of bacteria, which can lead to infection and subsequent bleeding. The fibrin clot is initially stable but eventually breaks down, allowing bleeding to resume. This phenomenon is often referred to as "fibrinolysis."

**Why Each Wrong Option is Incorrect**
**Option A:** Within 24 hours is considered primary haemorrhage, which is a different entity altogether. Primary haemorrhage occurs immediately or shortly after surgery due to technical errors or excessive bleeding during the procedure.

**Option B:** After 2 weeks is too late for secondary haemorrhage, as the risk of bleeding significantly decreases after this period.

**Option D:** After a month is even more unlikely, as the risk of bleeding continues to decrease over time.

**Clinical Pearl / High-Yield Fact**
It is essential to monitor patients closely for signs of secondary haemorrhage, including excessive bleeding, pain, or difficulty swallowing, especially during the 5-10 post-operative days. Early recognition and prompt treatment are crucial to prevent severe complications.

**✓ Correct Answer: C. 5-10 post operative days**