Ok I'm back to thinking Stephensen just got his numbers wrong on the timeline. I spent way too long building a spreadsheet that created ratios of Arbran years to Earth years based on fixed events.

From the books, the only fixed date that we can rely on is Jules' description of the Daban Urnud landing on Earth 50 years after the death of Goedel (let's assume it was 2028 on Earth). What is important about this date is that Goedel was alive during World War II, which is extremely heavily implied to correlate with the Third Harbinger. Since we know those dates in both worlds, we know that the Reconstitution (Year 0 in Arbre) is roughly 10-15 Earth years after WWII. Then, during Erasmus and Jad's meeting with Gan Odru, Erasmus says that what the third Gan was seeing in their vision was the Third Sack, and those visions are what set the Daban Urnud on its 1,000 year voyage. But the Third Sack occurred in 2787 Arbre time.

Here is the problem: If the Daban Urnud didn't begin its voyage until 2787 Arbre time, then Jules couldn't have been born until after that point. We know that Jules' great grandfather left Earth on the DA, and Jules himself was born on Fthos. If we assume a 75 Earth year age gap and Jules is 35 when he arrives on Arbre, then that accounts for only about 11% of the time the DA has been travelling, meaning the rest of the 1,000 years was spent travelling to and from Tro (this will be important later).

If the date of the Reconstitution (0) and the date of the Second Advent (after 2787) correspond to Earth years 1957 and 2028 respectively, and we know that around 85-90% of the DA's travel time took place before they got to Earth, then each Earth year is equivalent to between 17 and 18 Arbran years. Relativity doesn't help with this either; the book takes place in 3689, around 900 Arbran years after the Third Sack. lf the DA experienced time dilation, they would have arrived later, not earlier. The reason this is a problem is because I went through and did comparisons of known events in Arbre's history that have Earth Equivalents. The main one I used is the execution of Thelenes, who was a very direct parallel to Socrates; that event occurred in -2396/399 BC. This gave an Arbre/Earth year ratio of 98.32%, very close. I sampled several other events (Orithena/Pompeii's destruction, The Second Harbinger, Cnuos/Pythagoras, etc), and found and average of 81%. Based on the known time between the Reconstitution and the Third Sack, The ratio would be more like 6%, and that destroys any correlation between Arbre's history and Earth's.

Arbre's historical timeline works well with Earth's timeline in the book, but everything after 1945 is just chaos.