The kinetics of the disintegration of baker’s yeast cells in a bead mill is described as dp/dt = K. (P_m – P), where P is the concentration of protein released and P_m is the maximum protein concentration achievable. K is the first order rate constant and is 0.5 hr^–1 for the system studied. The time required for the release of 90% of the intracellular proteins will be ​