It settles right away, I was using it outside in my screened pool cage, on my orchids when a puff of wind blew it into my face.
I use it indoors, under cupboards and in crannys for ants and roaches here. Never had a problem with breathing it indoors. But if you're worried, maybe put all the plants in the bathroom with the vent fan running, and dust them all in there, then wait a few minutes to make sure the stuff isn't flying around. It's not allergenic, just an 'irritant'. In fact it's so benign, people take it as a dietary supplement.
Systemics have another drawback besides their latent toxicity. The bugs get resistant to them quite quickly. Just like people using antibiotics too often, if any bugs survive the first treatment then they reproduce and the young are resistant to the insecticide.
