you can get seeds that go from seed to smokeable in as little as 6 weeks! most takes 2-4 months after harvest, drying, curing. Some strains take just 3 weeks to veg, mine took 2 months! Again, I had no idea what the heck I was doing for the first 1 1/2 months of growing. I actually grew just one lady before my present batch ( I lucked out, getting a nice lady from a 4 seeds). But that was just stick in the dirt water I borrowed for that one an HID light. But now I just use 4 foot flouro fixtures so mine are into their 7th day of flowering, just 'weeded' out 3 males today. so am down to 16 plants so far. mine shoukld finish in about another 4-5 weeks(ish!) it really is unpredictible, especially with baggie seeds! you really won't know until further along when you start to veg. by then you'll kind of know how fast your own plants are doing and will be able to guessimate their harvest time.
I started germination of my babies on Nov 18, 2007.
I should harvest around March 19th give or take days so 3 months, then drying for about 2 weeks or so, then curing for about a month.
Total from seed to smoke for me (estimate) is about 4 months most guys here claim 2-3 months, but they buy good seed and have better setups. I'll be happy with my harvest, that's all that matters.