We truly don’t know how lengthy it takes. There have been attempts to attempt to date inclusions in numerous elements of diamonds, and people have largely been unsuccessful. It may very well be that diamonds form over durations as short a time as days, weeks, months to hundreds of thousands of years. Generally, as with many crystals that develop on the Earth, it isn’t a steady course of. The diamonds could start to develop and then there may be an interruption for some cause – a change in situations, temperature, pressure, supply of carbon, no matter—and so they could sit …