I'd mark my calender for 7 weeks from the 12/12 Started Flowering date. That lets you know you are getting close. 8 weeks and a few days is a good rule of thumb, but I hope you do not go by the calender or date or number of weeks, it is just another clue that you are getting close. At ABOUT seven to 8 weeks, you will notice the stigmas (white hairs) changing to red, or reddish brown, another clue you are getting closer to HARVEST TIME.
Go to Radio Shack, and buy a $9.95 LIGHTED (by batteries) hand held microscope if you do not have one..
You will use it to look at those trichomes. Under the microscope, look at the trichiomes on a bud leaf. They look like little clear
tall mushrooms and little clear SPEARS. They start out CLEAR.
There are charts at GROWFAQ, under HARVESTING, that show the trichs, under a microscope. If you harvest when the trichs are clear, you get a HEADY HIGH. If they are dark, you get a tied to the sofa, near death, can't think High.
ALSO a few days b4 Harvest, it is time to decide if you are going to FLUSH, and withhold nutrients to cleanse the taste. Many GROWERS advise placing them in total darkness two days before Harvest too. That is debatable.
I strongly urge you to be reading up on CURING and HARVESTing here at GROWFAQ. A lot of work wnet into that advise there. Very Important factors for Potency!
I was about to HARVEST at 8 weeks, with cloudy and dark triches, when suddenly my buds started growing little white horns or little fingers on them. I waited another week, and am glad I did!