I have tried this many times in the past, but have come to the conclusion that once it is ready, chop the lot and take it as it comes.
I found that once you remove large amounts of the plant and leave behind other bits to "finish off", the plant goes into shock of having the major parts removed already, the metabolism slows remarkably and you end up waiting weeks for the rest to eventually and slowly mature. They are never as good as the first harvest, possibly due to the prolonged and drawn out maturation, the slowed metabolism or just the complete shock of the previous removal freaking the plant out, but I suspect all three things play a combined part in producing second rate buds from the second pick. If 90-95% of your plant is great, the 5-10% that isn't doesn't really matter. The smaller bits can be used for edibles and/or combined with your trim, saved for a rainy day or just given away to a friend in need. Even if it isn't prime, I don't know many people that say no to free buds, even if they are a bit small or "not prime". You never know, the universe is strange, most often that friend you give free buds to will one day come around with a bud or two and say, "remember when you gave me....."
Hope this helps,.............
Organoman.