Final answer:
The Fries Duty Timer interval after which it sounds can vary and needs to be confirmed with the restaurant's operation manual or the manufacturer's instructions. Without context, it's impossible to provide the exact timing.
Step-by-step explanation:
The Fries Duty Timer is a device used in fast-food restaurants to monitor the cooking time of fries. The specific time after which a Fries Duty Timer will sound can vary by the restaurant's policy or the manufacturer's settings. However, for this question, without additional context on a specific restaurant or timer brand, it is not possible to provide an accurate answer as to whether it would be 120 seconds (Option A), 180 seconds (Option B), 240 seconds (Option C), or 300 seconds (Option D). It is recommended to refer to the restaurant's operation manual or the manufacturer's instructions for the precise timing.