8 weeks flowering

The decision when to harvest should not be done according to how long it has been flowering but according to the bud growth and trichome coloration - First indication that your plant is nearing harvest is when the buds have noticeably stopped growing and fattening, then you should check for the trichome coloration and decide when to harvest according to the ideal effect of your bud (clear trichomes are immature and have low potency, Milky/cloudy trichomes indicate mature trichomes with high THC potency which gives a more head "Sativa" high, then there's amber/orange trichomes with degrading THC that turns into CBN that gives you the more relaxed and sedating "Indica" effect. Of course if you have no way to check trichomes you can also roughly determine harvest according to pistil coloration which is recommended at about 70-80% orange/brown (although this varies between strains and very inaccurate). Hope this helps! Good luck and happy growing :)

We cannot know. You should learn to inspect the trichomes on the buds and see if the plant is done or not. Id say 12 weeks minimum for autos but it can depend on the strain. Only way to know for sure is to get a pocket microscope or loupe and check the trichomes on the bud, if they are mature the plant is ready. Keep in mind not all buds mature at the same time; its up to you to decide if you want to do progressive harvest or all at once.