I used to use the % of "red hairs" to determine harvest time, BUT,,,,,,, since joining 420, I learned IT'S ALL ABOUT THE TRICHOMES!! I can't tell by your yellowish picture, you need to look though at least 40X magnification to see if your TRICHOMES are optimum colors. It's hard to wait for Amber to appear in your trichomes, but that's what tells you, it's time to harvest. You can see this on your buds with a 5 dollar microscope.
this bud went a little too long, it has maybe 40% Amber trichomes, this will glue me to the couch! just Google "trichomes" and click images, you'll see a chart explaing it better than I. Looks great so far!