The planet Rukbat 3 was surveyed about 200 years before settlement ("Landing").
These stories are set before and during the First Pass, from just before settlers landed on Pern until about fifty years afterward (0 to 50 AL).
Just after the First Pass, 58 years after landing.
Just before and during the Second Pass, about 250 years after landing.
Just before and during the Third Pass, about 500 years after landing.
Late in the Sixth Pass, about 1550 years after landing.
Just before and during the Ninth Pass, about 2500 years after landing.