I dont know if ure a new grower or not but from what I see and learned myself from trial and error, is that most noobs follow the breeder guideline to the t on when to harvest. My first few grows said 8 weeks and I cut exactly at 8 weeks. Could have easlily went 9-10 weeks. Initially I was taught to watch the hair technique. This actually works better than the breeder guideline.After 7 grows and hundereds of hours of research and book reading, I think I must agree with using a microscope for your ripeness time. I have a Kandy Kush going that says 9-10 weeks flowering. I have past 70 days (10 weeks) and my trichs are about 70% milky,25% clear, and 5% amber. The leaves r yellowing and curling. I could take her now and guarantee that if properly dried and cured she will bust my head.
My main point is be patient. Dont rush your harvest and it will reward you tremendously. Hope this helps you out a little. That sour kush is more sativa I think. If it is, 9 weeks seems short for a sat dom plant. But let others chime in on this. These r just my opinions.