When Does "Endymion" (1996) Take Place?
"Endymion" is a science fiction novel written by Dan Simmons that released January 16th, 1996. So when is "Endymion" set?
It takes place in the years:
We know this because Raul Endymion tells the reader very early on, "I was born on the world of Hyperion in the year 693 ADC on our local calendar, or 3099 AD, pre-Hegira reckoning, or, as most of us figure time in the era of the Pax, 247 years after the Fall." Soon after, we learn, "At the time my life changed forever and this story really begins, I was twenty-seven years old", making it currently 3126 AD.

3126 AD - 3127 AD
We know this because Raul Endymion tells the reader very early on, "I was born on the world of Hyperion in the year 693 ADC on our local calendar, or 3099 AD, pre-Hegira reckoning, or, as most of us figure time in the era of the Pax, 247 years after the Fall." Soon after, we learn, "At the time my life changed forever and this story really begins, I was twenty-seven years old", making it currently 3126 AD.
3099 + 27 = 3126.
Furthermore, partway through the narrator describes Raul's record as "whereabouts unknown until less than ten standard months ago, Ascensionmonth 23, A.D. 3126, when..." and describes the early part of the story.
Around three-quarters of the way through the book, Cardinal Simon Augustino Lourdusamy says, "As I said to you one year ago..." then refers to a previous conversation less than one quarter in. Therefore the narrative covers, at least, 1 year. So we end in 3127 AD.
3126 + 1 = 3127.
[HOWEVER, the phrase "after the Fall" could refer to the time since the events of the previous novel "The Fall of Hyperion" (1990), which takes place in 2764 AD. If so the main character was actually born in 3011 AD and the present of the novel when he is 27-years-old is 3038 AD and 3039 AD at the end.
2764 + 247 = 3011
and
3011 + 27 = 3038
and
3038 + 1 = 3039.]