How Long Does It Take for a Drug and Alcohol Rehabilitation Program to Last?

I want to undergo a drug and alcohol rehabilitation program. I want to start over with my life and I think allowing myself to be sober and detoxified is my first step to recovery. I’m worried about the time, though. I want to know how long the program will last because I want to be fully-recovered by the time my sister Sam gets married (which is in 6 weeks). Please help. Thank you.