The maturation cycle was a duration of time in which children who had been assimilated by the Borg were placed into a maturation chamber for. According to Seven of Nine, these children were placed there for a period that lasted for seventeen cycles. (VOY: "Mortal Coil")
The 29th century drone One completed its maturation cycle from infant to adult in one day. Following the completion of the maturation cycle, One's first words were "We are Borg. State our designation," thereafter, he awaited his instructions. (VOY: "Drone")