When I put SD in a new tank set-up, I waited about a week and it did not settle. Added some filter floss in an aquaclear filter and cleared it up in a day.
Mine turned slightly milky, I went through 3 micron cartridges in my magnum350 Cartridge filter. It was completely clear in 3 days. I did then have to take all my equipment completely apart and clean it really well.
But---
I put my sand in a trashcan and did 90% waterchanges on it every couple days for a month before adding it too my tank.