The formation of Pluto's moon Charon is thought to have occurred shortly after the formation of Pluto itself, during a giant impact event. According to current theories, Charon is believed to have formed when a large object, possibly another planetary body, collided with the early Pluto. This impact was powerful enough to eject material into orbit around Pluto, which eventually coalesced to form Charon.
While the exact timing is uncertain, scientists estimate that this impact event and the subsequent formation of Charon took place within several million years after the formation of Pluto. This relatively short timescale is supported by computer models and simulations of the early Solar System's evolution. However, it's important to note that our understanding of these events is still evolving, and ongoing research and discoveries may refine our knowledge in the future.