Biological half-life by route of exposure
             It has a plasma half-life ranging from 3 to 6 hours
             depending on urinary pH (Parfitt, 1999).
             No change in half-life from that seen with therapeutic dosing
             was observed in an otherwise healthy patient with massive
             overdose (Snook et al., 1992).
             The ephedrine concentrations in three fatalities were 3.49;
             7.85 and 20.5 mg/L (Ellenhorn, 1988).
So I'm thinkin 24-48 to be on the good side..