Start your flush when there are about 95% brown/orange pistils.
The pistils turn brown as the plant ages, while there are still many white pistils it indicates that the flowers are still young and growing.
Once most of the pistils have turned brown, the flowers will be mature and "adult" like and ready for harvest.
From your pictures, I would say you have 3 or more weeks until these flowers will be fully grown and "adult" like, at the moment they are still "teens".
The pistils tell you everything about the plants maturity/ripeness.
Hope this helps, Organoman.