**Core Concept**
The question is testing the student's knowledge of the timeline of reactive astrocytosis in the cerebral cortex following a non-hemorrhagic infarct. Reactive astrocytosis is a hallmark of astrocyte response to injury, characterized by the transformation of astrocytes into a reactive phenotype, which is essential for the repair and scarring process.

**Why the Correct Answer is Right**
Reactive astrocytes can be seen as early as 24-48 hours after the insult in the cerebral cortex. This is because astrocytes are one of the first cell types to respond to injury in the central nervous system. The astrocytes undergo a rapid transformation, characterized by changes in their morphology, gene expression, and function. This transformation is mediated by various signaling pathways, including the activation of transcription factors such as ATF3 and c-Jun. The reactive astrocytes play a crucial role in the clearance of debris, regulation of the extracellular environment, and promotion of neuronal survival.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too early for reactive astrocytosis to be observed. Astrocytes may start to show signs of reactivity as early as 6-12 hours, but the full-blown reactive phenotype typically takes 24-48 hours to develop.

**Option B:** This option is incorrect because it is too late for reactive astrocytosis to be observed. While reactive astrocytes can persist for weeks or even months after the insult, the initial response typically occurs within 24-48 hours.

**Option C:** This option is incorrect because it does not accurately reflect the timeline of reactive astrocytosis. While astrocytes may start to show signs of reactivity within 6-12 hours, the full-blown reactive phenotype typically takes 24-48 hours to develop.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that reactive astrocytosis can occur in various types of cerebral insults, including ischemic stroke, traumatic brain injury, and infections. This makes the study of reactive astrocytosis an essential aspect of understanding the pathophysiology of these conditions and developing novel therapeutic strategies.

**Correct Answer: C. 24 hours**