You need to know your strain and keep track of your weeks as a general reference so you can gauge when you begin your flushing. When you notice there not a lot of new white pistil growth, you are really close to done. When you see your leaves start turning fall colours, you are close. But the best method to go by is to examine the trichomes. You need a Jewellers magnifying glass. About 60x is good. Inspect the resin glands for their clarity and colour. You want mostly cloudy resin heads with some amber. There will always be a few clear ones but mostly you want to see them appear cloudy with a few ambers. If you see that, your ready for harvest.
Judging from your pictures, i would say you should start to flush out the soil of nutrients which is what you should be doing when you are 2 weeks from harvest anyway.