What is holdover time?

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Holdover time is the period after de-icing/anti-icing fluid has been applied during which the fluid is expected to keep the aircraft surfaces free of ice under the current weather conditions. It begins once the application is complete and ends when the protection is no longer effective due to ongoing weather effects like precipitation or temperature changes. This is why the correct option describes it as the time remaining before de-icing/anti-icing protection expires. The duration depends on the fluid type used and the environmental conditions (temperature, precipitation type and intensity, wind, etc.). It isn’t the time to apply the fluid, nor the engine run-up, nor a fueling window. In practice, departures must be planned to occur within holdover time, and reapplication is needed if the holdover time expires or conditions worsen.