Hi, thought I'd put in a briefish timeline
of Significant Events in the 'Culture' Galaxy

Based on the 'Culture' novels, some dates can be estimated
or ascertained based on some specific dates given:

Homo Sapiens evolves on Earth 200K BCE

Beginnings of language and self-awareness in H.Sapiens 180K BCE

Beginning of Idiran civilisation 40K BCE

Explosion in Art on Earth c.33K BCE

Homomda enter galactic scene c.14K BCE

Beginnings of Human/Humanoid/Panhuman civilisations
on several thousand planets and habs c.13K BCE

Civilisation on Char's World self-extinguished c.10K BCE

Several humanoid species become space-faring c.9K BCE

[1000 years later they invent 'Marain', a synthetic
language later used by The Culture]

[2000 years later these species form the space-faring
elements of The Culture]

First planetary civilisations join The Culture c.5K BCE

Culture citizens commonly existing in Virtual Forms c.4500
to 3900 BCE
(assumption based on "Look to Windward" and probable 600 year
lifetime of fads)

Brief terraforming period by the Culture c.3900 to 3300 BCE

First 'Orbital' under construction by the Culture, founding
of 'Contact' and 'Special Circumstances' c.700 BCE

General Contact Units still Captained at this time c.625 BCE
(2500 years before "Excession")

First Culture Mind constructed c.500 BCE

Birth of Christ on Earth (concerns "The State of the Art") by 1 CE

Chelgrian Unification Wars c.170 CE

First of four disputes between Culture and Idirans 1267 CE

Formal beginning of Idiran-Culture War 1327 CE

("Consider Phlebas" set in the war's early years)

Homomda enter Idiran-Culture war on Idiran side 1332 CE,

General Offensive Unit 'Limiting Factor' constructed c.1367 CE
(716 years before "The Player of Games")

Battle of Twin Novae in Arm One-Six 1367 CE
("Look to Windward" is set 800 years later)

Formal end of hostilities between Idir and Culture 1375 CE

Chelgrians achieve 'Involved' status in Galactic terms;
4% of Chelgrians Sublime and thus become the 'Chelgrian-Puen'
[16th century?]

Perosteck Balveda leaves Storage along
with millions of other Idiran War Veterans 1813 CE
("Inversions" probably set a generation after)

Diziet Sma explores Paris and Berlin on Earth 1977 CE
("The State of the Art)

Contact made with Earth c.2110 CE

Chelgrian Caste-War ends c.2152 CE

Novels confirmed to be set between 1330 and 2110 CE:
"Consider Phlebas" c.1330
"Inversions" c.1840
"Excession" c.1875
"The State of the Art" 1977
"Player of Games"-c.2081
"Use of Weapons"
("Slight Mechanical Destruction" wrote/set 2089
[Khmer year 115], most of the novel is set before this
date)

Novels and novellas set roughly before/circa 2110 CE:
"Descendant"
"A Gift From the Culture"
"Matter"
Novels set after 2110 CE:
"Look to Windward"-c.2167