**Core Concept**
The question tests understanding of **oral rehydration therapy**, specifically the preparation and storage of **oral rehydration solutions (ORS)**. Freshly prepared ORS has a limited shelf life due to the risk of bacterial contamination.

**Why the Correct Answer is Right**
A freshly prepared ORS should not be used after 24 hours, as it can become a medium for bacterial growth, leading to potential infection. The World Health Organization recommends discarding any unused ORS after 24 hours.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too short a timeframe.
**Option B:** This option is also incorrect as it exceeds the recommended timeframe.
**Option D:** This option is incorrect as it is not a standard recommendation.

**Clinical Pearl / High-Yield Fact**
Remember, ORS is a lifesaving intervention for **dehydration**, particularly in children with **diarrheal diseases**. Always follow proper preparation and storage guidelines.

**Correct Answer:** D. 24 hours.