In the past, I experimented quite a bit depending on what effect I wanted for the final product. If the buds were developed enough I have harvested plants with almost no amber, and with a nominal 20%+ clear trichs for the zoom. And opposite of that, I have waited and harvested plants that have had 20%+ amber in hopes of a sleepy couch locking buzz. Lately, I just wait for about 5-10% amber.
I have taken quite a few to far older than breeder specs (including Mephisto), and doubt that I have ever seen as much as 30%. I'd love to get more sleep effects, but worry about leaving them too long.