Some plants will ripen from the top down, and some will finish in the opposite yielding ripened flowers first from below. This is something I've observed through many years and varieties. 

When I began growing there was little literature to be found and I knew nothing about trichomes and there development beyond just the basics of what they are and what's within. I learned through this that a calendar is just a rough guideline and the subtle of difference can change the harvest window.

Some varieties will retain clear trichomes and these are often Narrow Leafed Drug type (Sativa) and degradation takes place then in the formenting and curing process traditionally. I've seen in the opposite spectrum Wide Leaf Drug types with Amber trichomes and fully developed flowers as early as 42 days. These types I believe have an almost auto flowering quality that I've learned hail's from some of the Northern Afghanica varieties that are not just utilized for hash production and utilized for fiber, seed and more. 

In conclusion there's a lot to learn about Cannabis flowers and their development and the harvest window, especially if you are growing multiple varieties or just a plethora of today's Polyhybrid x Polyhybrid types. I do prefer just about every type of Cannabis to be taken to the fullest of its potential and for me regardless of it being Narrow or Broad Leafed I really like my flowers to be fully developed and mature as possible with most averaging around 10 weeks of Flowering time give or take a few days..