Thanks, everyone!  So it sounds like they should be harvested about when a regular THC plant would be:  with mostly cloudy trichs.  Think I can manage that!  
 
I always use the overall look of the plant (pistils, trichome coverage, texture, color, etc) to determine when to harvest.  Trichome color is secondary & I can't see it all that well with my crummy magnifying glass anyway.  But the estimated harvest date is 70 days so I'll probably stick pretty closely to that & hope for the best.  I did a pretty good guesstimation with my first grow, though it wasn't a CBD-heavy strain.