Which method will decrease the holding time during anti-icing when using a two-step process?

Applying heated Type 2 fluid is the method that will effectively decrease the holding time during anti-icing in a two-step process. Heated Type 2 fluid is designed to have a lower freezing point and better performance in preventing ice formation. The elevated temperature allows the fluid to spread more effectively and maintain its properties longer in colder conditions.

Unlike Type 1 fluids, which primarily de-ice and then must be reapplied, Type 2 fluids are formulated to provide longer-lasting protection when heated. This means they adhere better to surfaces and can resist ice formation for an extended period, directly reducing the required holding time. It enhances the efficiency of the anti-icing process by working effectively at lower temperatures, ensuring a more reliable protective layer.

The other options do not specifically address the core issue of improving the effectiveness of the anti-icing process in relation to holding time. Decreasing the water content might not necessarily enhance performance, increasing viscosity may hamper the fluid's ability to flow and cover surfaces adequately, and simply increasing the application rate of Type 1 fluid would not guarantee improved hold time since Type 1 fluid is primarily for de-icing, not anti-icing. Thus, applying heated Type 2 fluid stands out as the most effective choice.