In my smaller tanks, it usually takes about a day or two. In my 30, I managed to keep it from going through the cloudiness by taking 5 gallon bucket fulls outside and running a hose through it. Fill the bucket up, slosh it around and empty it. Did that SEVERAL times until all the smaller particles we're rinsed out. I was left with nice, clean sand. I used pool filter sand, though...
HTH.