Dress the salad just before serving; cucumber releases water and thins the dressing as it sits. If preparing ahead, keep the vegetables and dressing separate. Refrigerate leftovers promptly in a sealed container at 4°C (40°F) or below and eat within 2 days; the cucumber will soften. Discard salad left at room temperature for more than 2 hours, or more than 1 hour when the temperature exceeds 32°C (90°F).