## Core Concept
The question pertains to the concept of myocardial ischemia and the timeline for irreversible injury in the myocardium. Myocardial ischemia occurs when blood flow to the heart is reduced, preventing the heart muscle from receiving enough oxygen. This can lead to cell injury or death if prolonged.

## Why the Correct Answer is Right
Irreversible injury in the myocardium occurs when the ischemic event persists beyond a certain threshold, leading to cell death. This typically happens after 30 minutes of ischemia, but it can vary depending on factors like the presence of collateral circulation and the metabolic demand of the myocardium. The correct timeframe for irreversible injury is generally considered to be around 30 minutes or more of ischemia.

## Why Each Wrong Option is Incorrect
* **Option A:** Less than 10 minutes - This duration of ischemia is typically not long enough to cause irreversible damage. The myocardium can often recover from brief periods of ischemia.
* **Option B:** 10-20 minutes - While ischemia for this duration can cause significant injury, it may still be reversible with prompt restoration of blood flow.
* **Option D:** More than 2 hours - Although more prolonged ischemia will certainly cause irreversible damage, the timeframe for irreversible injury to begin is actually shorter.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the myocardium is very sensitive to ischemia, and timely intervention (such as with thrombolysis or primary percutaneous coronary intervention) is critical to limit damage. The concept of the "ischemic penumbra" is also important, where areas of myocardium are at risk but not yet infarcted, and can potentially be salvaged.

## Correct Answer: C.