How long does concrete dust take to settle
Concrete dust becomes air-bourn when it is pulverized (due to tool use: drilling, sawing, hammering, etc.). The fine silt concrete dust is thrown into the surrounding air by electric tool motor fans or other air currents. The particulate is so small and light-weight any slight breeze will distribute it until it finally sinks and lands on a surface.   Where, when, and how long will depend on too many extenuating circumstances to even guess at. The best way to deal with any dust becoming air-born is to stop it before it happens. I've found a shop-vac held just above the concrete surface that is being worked on does a smashing right good job at eliminating dust.