Yes, staggered harvests are possible, but be aware that the remaining flowers will take a lot longer to mature due to the removal of large sections of the plant causing a metabolic shock. Basically, this means there is less plant left to provide energy for the remaining flowers to ripen as fast as they were previously, when the plant was entire. If time is an issue, harvesting the entire plant is your only real option, but if you have time to wait, harvesting the tops and leaving the lower parts longer will be ok. In my experience though, the remaining flowers take 2-3 longer to finish than the expected rate of ripening. The second harvest flowers also never seem quite as good as the first harvested flowers and I suspect that due to the shock of half a plant going "missing", combined with the corresponding reduction in energy production (photosynthesis) and slowed metabolism, all contribute to second rate flowers that just don't have the punch of the flowers from the initial harvest. These days I just harvest the whole plant and deal with what I have got and not worry about "what could have been". Learning from this, it teaches how training your plant, combined with some "lollipopping" can result in a much more even harvest maturity, throughout the entire plant. I have also found that people generally are very happy to receive some free "not quite prime flowers" any time they are offered, especially some one who is a bit down on their luck at that time. It is amazing what some free buds will do to lift a persons spirits!! Otherwise you could make some cannabutter or various extracts with the "not quite prime flowers", but giving it away, really is a good feeling!
Hope this helps,..... Organoman.