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Immunochromatographic assays must be interpreted strictly within the manufacturer’s read window. After that period, evaporation and non-specific binding can create “evaporation lines” or color changes unrelated to true antigen–antibody reactions. A line appearing only after the allowed time is invalid and must not be reported—repeat the test following instructions exactly (timing, specimen volume/temperature). Option C reflects proper POCT practice. Option A ignores timing and risks false positives. Option B misstates the issue; faint TRUE positives within the window are valid, but late-appearing lines are not. “Borderline” (D) is not a manufacturer category for late reads. Maintain QC (external controls at defined intervals and with new lots), store kits per temperature/humidity specifications, and document any invalid runs and repeats. Adherence to timing is a key quality element for waived testing emphasized on certification exams.