The Preserver Era was the name given by historians of the 23rd century to the period of history in which the Preservers were active. This lasted from 38,000 BCE (reference stardate -400/00) to 18,000 BCE (stardate -200/00).
At this time, local space was in a relatively quiet period. There were only a handful of technologically advanced civilizations around, and most of them were planet-bound. (FASA RPG module: The Orions: Book of Common Knowledge)