Happy 420 Hypo! you've made it this far, don't freak out now! just keep on it. WW goes 8-11 wks in my garden, how far are you now? just listen and look at your girls. They will tell you when their done. I had plenty good results just by waiting and patience before I ever bought a Microscope. When they look totally done (lots of red hairs, i mean ALOT! and no possible room to bulk up within the buds to were they poke out on the sides.....then take out the microscope. ...if you wanna get technical.) A bagillion trillion million growers in the 70's and 80's grew killer weed without one. I'm not saying that you shouldnt use one or anything, but just keep that in mind. use that knowledge as a base and work up from there. Who really cares (or will notice in the long run) if you don't wait until the perfect exact mega-perfect-instant.) If your growing for yourself you will still get high/medicated, and if your growing clones of that plant you'll know more about it and how it reacts/yields/how long it takes next time. Personalyy I believe that the "exact time" is a myth. It's more of a good guideline than a rule.
This is just my opinion, but I hope it helps.