Hailstones are formed in high altitude clouds at 253 K. Consider a hailstone with diameter of 20 mm and is falling through air at 15°C with convection heat transfer coefficient of 163 W/m² · K. Assuming the hailstone can be modeled as a sphere and has properties of ice at 253 K, determine the duration it takes to reach melting point at the surface of the falling hailstone.