Through 35+ years of experience, I have come to the conclusion that partial harvesting does not work, unless you are waiting for seeds to mature.
It is best to harvest the whole plant all at once and take it as it comes.
It seems that when partial harvesting, the removal of large parts of the plant freaks it out, resulting in the remaining flowers taking ages to finish and nowhere near the same quality as the first picked flowers. I believe this is due to the massive disruption partial harvesting causes to the plants metabolism that freaks it out and prevents the metabolism ever recovering, leading to sub standard buds on the second lot of harvested flowers. It is a bit like expecting a Vee Eight racing car to continue lapping at the same times after 4 of its cylinders have been disconnected.
Hope this helps, Organoman.