It depends on the strain, if your asking how long to flower. I would say the bulk would fall into the 7-10 week range. If its a sativa strain then it would be up to 14 weeks. I have heard even longer in some cases.
Some growers will start counting from day one of 12/12 others wait till they see the first signs of gender.
Now if your asking when you might see flowers they usually show in the first two weeks,