657,209 AD is the year visited by The Time Traveler on one of his visits to the future.
Original timeline[]
During the Time Traveler's first trip into the future, he passed through this era without stopping, but he certainly didn't notice the sun going out; This caused much surprise upon his arrival during his later trip to this year. ("The Time Machine")
Altered Timeline[]
After telling his friends in the 19th century about his trip to the future world, he unknowingly created an alternate timeline. In this new timeline, humans had constructed a massive sphere around the sun, which became their new primary habitat. Physically, they had genetically engineered themselves into Morlocks by coincidence; they had never encountered the Morlocks from the original timeline. Nebogipfel befriended the Time Traveler after he arrived in this year and became his time traveling companion. ("The Time Ships")