4 to 5 weeks depending on genetics. What kind of light are you using? You'll need more light for the later stages of flowering.. or at least ull want it. Do you keep it by the window? That would probably help, the light is 12/12 outside (where im at). Look for some big 40w CFLs they should be the equivalent of a 150w halogen bulb. They usually are around 2500k-3500k and are pretty good for flowering. Are u giving her flowering nutrients? and what kinda pot/potting soil are u using?