Should I start to flush?

Hi! Looking at your photo, it seems you still have majority of milky trichomes, so you may have to wait one or two more weeks. Use a microscope to look at the trichomes aspect. The oldest leaves must start to yellowish too, it means she's going into senescence. Power Clean from Bio Technology (usable in organic) is supposed to "accelerate the senescence process of the plant by sending it a strong EOL signal". So if you're in a hurry, you can try it. And don't fully flush your plant : you use vegetal nutrients so not feeeding them the last week is enough (water + Elycitor is my way).