Hi bro, the rate of production of this ppt will be limited by the amount of anaerobic bacteria you have. Usually this develops about 3-4 months of having a sandbed but technically, this process will occur as long as you have a very deep sandbed.
It is not advisable to have too many organisms to disturb the sandbed as you disrupt the oxygen diffusion rate for any specific area and ultimately disrupt the different zones. Remember, the bacteria we are talking about here is facultative