After flipping through the thread, here is my opinion.
Most 8 week strains are usually more like 60 days, which is only 4 more days than advertised. When they say 8-9 weeks... they really mean just that, more than 8, less than 9... and most of the time these estimates are pretty good as long as the grow goes well.
I like to harvest my plants when there are very few clear trichomes. I have harvested early before and have found the cannabinoid profile to leave me wanting more... and usually with a headache a few hour later. I have harvested late and found the profile to be lacking in other ways, and having a noticeable ceiling where I just can't get higher no mater how much I smoke.
My personal preference is to harvest when there is only 1-2 clear trichomes for every 8-9 cloudy and/or amber trichomes. 10 to 20% clear.
I find that the ripening is a snowballing effect. Starting out fairly slow, but increasing over time. The whole plant can change in 10 days, easily, so just keep your eyes peeled and aim for between 8 and 9 weeks and not 8 weeks exactly.