It's a good question, and a tricky one. The half-life is the time taken for the concentration of the drug to reach half its original level (so not the same as the time taken to completely clear your system.)
People vary in the time they take to actually metabolize the drug after taking it. Some take half an hour to reach peak plasma level, and some take up to 10 hours. Once it
reaches a peak level in the body it then takes roughly another 2-3 hrs for the drug to halve in concentration (whether you take 3mg or 9mg) . But, some of the drug will remain in your system for many hours after that...