Which of the following does NOT influence the accuracy of HGN test results?

The factor that does not influence the accuracy of HGN test results is the time of day. Horizontal Gaze Nystagmus (HGN) testing is primarily focused on specific physiological responses of the eyes, which remain consistent regardless of when the test is administered.

In contrast, the other factors listed—subject's age, alcohol level in the blood, and lighting conditions—directly affect the performance and results of the HGN test. For example, the subject's age can impact the presence and degree of nystagmus; individuals may exhibit different responses as they age. The blood alcohol level is crucial, as higher levels can significantly increase alcohol-induced nystagmus, making detection easier or more pronounced. Lastly, lighting conditions can affect visibility and the examiner's ability to accurately assess eye movement, which is essential for a valid HGN evaluation. Therefore, time of day does not play a role in the physiological responses measured in the HGN test, making it the correct choice in this context.