As an American who has gotten very used to metric units in studying engineering, the general rule I picked up is that you typically only change units every three orders of magnitude. So 8 decameters would typically be expressed as 80 meters, maybe 0.08 kilometers. Decameters and hectometers are a thing, but they’re not common units. Even centimeters don’t see much use compared to millimeters.
Wikipedia lists influencer as a synonym for internet celebrity, so I guess just when they become famous.
Unless you take the title literally, then it’s whenever they become influential over a statistically significant portion of the population.