Leromeanswered grow question 8 days ago Usually every cannabis plant develops "preflowers" between the third and sixth week of its life. Those are a sign of beginning of sexual maturity, its like puberty for humans. An automatic plant will begin to create flowering hormones from there on, since its not dependant on the photoperiod. You should see a "stretch" in growth and more calyxes and stigmas being developed on the top part. Flowering has now begun. Automatics dont like to be restricted in the root zone. This aswell as other stressors may trigger an early flowering. Thats why you want to start automatics in big pots/end pots and stress them on the low side only.
Photoperiodic plants will show signs of sexual maturity after the third and sixth week of its life aswell, but it does not mean that she will go into flower, it only shows the sex/gender and maturity of the plant. You can force them to flower before this by reducing the light to 12/12, they will have a bigger stretch the earlier you flip them though and mature plants tend to be more potent and have a greater yield. So its best to flip after preflowering, especially when using regular unfemininzed seeds to get rid of the males.
It may take anything from 3 to 14 days for preflowering plants to go into flowering, depending on many factors. The biggest factor is probably again the veg. time, short veg = more stretch and longer preflowering period, longer veg = less stretch and shorter preflowering period meaning your plants switch into flowering quicker when flipping after preflowering.
Hope this helps, happy growing!