**Core Concept:** Nosocomial infections are infections acquired by patients during their stay in a healthcare setting, not present at the time of admission. These infections can be categorized into early-onset (occurring within 48-72 hours of admission) and late-onset (occurring after 48-72 hours of admission).

**Why the Correct Answer is Right:** The correct answer (C) is "48-72 hours of admission." Nosocomial infections are typically classified into early-onset and late-onset infections. Early-onset infections occur within the first 48-72 hours after admission, while late-onset infections manifest after these initial 72 hours.

**Why Each Wrong Option is Incorrect:**

A. This option (24 hours) is too short to account for the typical onset of nosocomial infections, which typically occur within the first 48-72 hours.
B. This option (72-144 hours) is too long and does not differentiate between early- and late-onset infections, which have distinct timeframes.
D. This option (more than 72 hours) also does not accurately differentiate between early- and late-onset infections, which occur within the first 48-72 hours and after 72 hours, respectively.

**Clinical Pearl / High-Yield Fact:** Understanding nosocomial infection classification is crucial for appropriate treatment planning, resource allocation, and infection control measures in healthcare settings. Early-onset infections require different interventions compared to late-onset infections. Monitoring patients for signs and symptoms of infection within the initial 72 hours of admission is essential for timely diagnosis and management.