Dreads are a natural occurrence when hair is left uncombed and unconditioned over a period of time. Pure neglect, or Nazarene locks receive no maintenance except washing. typically they are allowed to form any way they form without any control.
This might not be the best way for all who choose to go natural. A more controlled form of natural dreadlocks still embraces the minimal maintenance philosophy, but adds separating (ripping) to prevent congos to the routine dreadlocks maintenance.
Natural dreadlocks can often form fairly quickly, within a few weeks, however can sometimes take much longer.
The estimates many sites state are used as a scare tactic to scare you into buying products and choosing quicker methods. for more info see the Dreading methods section of the dreadlock forums as well as the natural/neglect dreadlock group