At this stage, you could already harvest, but this is the method I use. When most of the trichomes β around 50β70%, like I see in your photo β turn milky, I start flushing with plain water. I flush for about 7 to 14 days, depending on the plant size, substrate, and other factors.
By the end of those two weeks, it usually develops a few more amber trichomes β around 20β30% amber total β and that ratio works perfectly for me.