Cefotetan is a cephalosporin antibiotic with activity against most Gram-positive aerobic organisms and some Gram-negative bacteria. A patient is receiving 1 gm cefotetan q 12 hr administered as a short infusion of 0.5 hr duration. How long it takes to achieve steady state ? (Cefotetan Vd is 12 L and k is 0.2 hr-1 )