Usually when they start eating solids. So, for the kids here, first 24hrs are the meconium, and from 1-3 weeks its the yellow milk poos which sometimes looked like clumped pellets, but they are still soft. 2 weeks and onwards once they are eating hay, grass, grain, whatever solids. They will become darker and then shortly after they will be normal pellets. Normal poo for 24-48 hours is the black tar poo(meconium) and from 2 days to whenever they start eating solids is a soft yellow poo. Not usually hard, but also not runny. Any off colors, runny poo, or excessive mucus and I will start looking into there might be an issue.