Those plants look pretty nice, great job with your grow. Coco does flush easier than soil, I typically like 7 day flush, but 5 days will be enough if you give it some heavy waterings.
To determine when to harvest, you will want to look at the trichomes on the buds. You are looking at the color of the round head of the trichome. General rule of thumb is to harvest when you have 10% amber, 80% milky and 10% clear trichome heads. After a few harvests, you may find your own preference.
The amber heads are reported to have more of a sedative, body effect. The clear heads have been reported as being more cerebral and energetic high. Either way, you'll want the majority to be milky. These effects can be attributed to the maturation process of cannabinoids within the trichome heads.
Do be sure to check the buds and not the leaves. Trichomes on the leaves will mature faster than the buds, so they aren't the most accurate ripeness indicator you can use. However, they can be a good visual indicator as to when you might need to begin your flush if you choose to do so. Using a jewelers loupe is preferred, but many times you can use the camera on your phone to get a close up and clear picture of your trichome heads.
