According to Baldur’s Gate: Descent into Avernus, the Companion was summoned in 1444 DR, the Era of Upheaval.
In the relevant contract, it said that Elturel was doomed after 50 years from then.
That means the Fall of Elturel actually took place in 1494 DR, the Year of Twelve Warnings.
However, the Baldur’s Gate Gazetteer in the same module describes the city as of 1492 DR.
Interestingly, in the early-access version of the video game Baldur’s Gate 3 made by Larian Studios and approved by WoTC, which is a sequel to Baldur’s Gate: Descent into Avernus, the current year seems to be 1492 DR. To verify this, you could go north of the Risen Road to find a Tollhouse inhabited by some self-proclaimed Paladins of Tyr. In the basement, you will find a Tollhouse Ledger on the body of a dead Toll Collector, which states that the current year is 1492 DR.
Therefore, canonically, the event took place either in 1492 DR or 1494 DR, as far as I can tell. Has anyone settled this discrepancy? Which year is it?