A “drug patch” is designed to slowly deliver a drug (species A) through the body tissue to an infected zone of tissue beneath the skin. The drug patch consists of a sealed reservoir containing the drug encapsulated within a porous polymer matrix. The patch is implanted just below the skin. A diffusion barrier attached to the bottom surface of the patch keeps the surface concentration of the drug dissolved in the body tissue constant at 2.0 mol/m³, which is below the solubility limit of the drug in the body tissue. There is no difference in the solubility and diffusion coefficient of the drug between the healthy and infected tissues. The mean distance from the drug patch to the infected area of tissue is 5.0 mm. To be effective, the drug concentration in the tissue must be 0.2 mol/m³ or higher when it reaches the infected zone. Determine the time it will take in hours for the drug to begin to be effective for treatment. The effective molecular diffusion coefficient of the drug through the body tissue, both healthy and infected, is 1.0 × 10^-6 cm²/s.