You don't need to wait until it starts to foxtail. Usually that's a sign that it's cooking too long.
How you tell is by the pitils and trichomes. 90% cloudy is fine to start the flush on and the rest will cloud up come harvest. But really all comes down to how you like your bud? If its more sativa then harvest with 80% cloudy or if you like me and love an owl couch lock close to full cloudiness when coming near the flush/harvest.
You want 10-30% Amber pistils. (Hairs). And want them all curling back into the bud. Looking at your is a bit hard to tell. It looks done, but you got a few white hairs. Throw or cut feed and get ready to flush and bring her to harvest.
Good luck pal