I just read this:
Flowers are fragrant and last one to several days; they are pollinated at night by moths, although these plants are self-fertile (don't need a pollinator to make seeds). If you snap off the pods, you will get more flowers, but if you want seeds to make more daturas, let the pods remain. When the pods open, the seeds are ripe. I usually leave the pods on the plant until the pods turn brown, then harvest and empty the pods for the seeds.