I don't get the 1-2 per area. What is your area size. Anyways. Once you are pushing near 40+ days of flowering for an Auto, most are near done in that time. So once pistils showed, count down how many days she's been in flower and that'll give you an idea as to when your bud will be done, it's just a guideline now, all plants are dif. For instance I've had a plant I had to half harvest. She stopped feeding 2 weeks ago. As the top bud stopped drawing up food meaning the bud below is only getting water also. So if you have top heavy colas and larfy mid-low parts then by doing a little test from her run-off to see is she feeding. Your PPM should be down at least 2/3s to a half in that PPM, also it's a good thing to do, just to see if your plant is still feeding. If the PPM is higher than your feed then she's flushing herself. Now you'll need a clear base to see if she is still feeding. But it's just a good way to go if u have lots of uniformed bud sites or just need to see if she's still feeding, don't touch her.
Good luck.