A saturated clay layer of thickness $H = 4$ m has drainage at both the top and bottom boundary (double drainage). The coefficient of consolidation is $C_v = 2 \\times 10^{-7}$ m$^2$/s. The time factor is defined as $T_v = \\frac{C_v t}{d^2}$, where $d$ is the drainage path length. How many days are required to reach a time factor of $T_v = 0.2$ (approximately $50\\%$ consolidation)?