When Does "The Rise of Endymion" (1997) Take Place?
"The Rise of Endymion" is a science fiction novel written by Dan Simmons that released August 4th, 1997. So when is "The Rise of Endymion" set?
It takes place in the year:
We know this because a character awakes and asks, "How long was I buried there?" referring to events near the end of the previous novel, "Endymion" (1996), which ended in the year 3127 AD. They're answered, "Four Earth years".

3131 AD
We know this because a character awakes and asks, "How long was I buried there?" referring to events near the end of the previous novel, "Endymion" (1996), which ended in the year 3127 AD. They're answered, "Four Earth years".
3127 + 4 = 3131.
Additionally, there is a separate storyline in which a different character awakes and asks, "What year is it?" and a character answers, "The Year of Our Lord 3131". So it must be 3131 AD.
[HOWEVER, 4 years after an alternate date for the final events of "Endymion" (1996) would place this novel in 3043 AD.
3039 + 4 = 3043.]