I’m currently nearing the end of my second grow, each time with 4 plants (2 Northern Lights autos and 2 OG Kush Autos). The first time (with one each of 4 different strains), I harvested each entire plant at once (except for one plant, which I harvested in 3 batches over a couple of weeks). I waited until the uppermost buds had 20-30% amber trichomes, and then chopped the whole plant. The lower buds were not as “ripe” (less dense buds, fewer ambers), but I harvested them anyway.
In my second grow, which is almost finished (after >20 weeks since germination, and 16-17 weeks of flowering!), I started harvesting in early February. I took only the top buds when they had about 20-30% ambers, a few buds at a time, and then every few days (depending on the trichomes) took some more, and so on. I now have about 12-15 batches of buds from each plant - I’m already enjoying the first buds, while still continuing to harvest more.
It makes the grow more prolonged than harvesting all at once (and more $ spent on electricity), but I think the results will be a more uniform quality. I also find it easier to spread all the drying and trimming over several weeks than to have a massive pile of buds to trim all at once.