When were achievements, especially their timestamps, introduced to Steam?

I need to know for a project centered around achievements, furthermore the date they were unlocked. I want to mitigate the fact that some achievements before a certain date had no timestamps for statistical reasons.

The earliest indication of an exact date that achievements were assigned timestamps I could find is 2008-10-25 but I could not find any official statements so far. Is there an earlier known and/or even official date?

In addition, what's the exact date that Steam achievement became available in general (without timestamps that is)?

Solution 1:

According to a GiantBomb article Steam achievements were introduced with The Orange Box, which was released 2007-10-09. Half-Life 2: Episode Two, Portal and Team Fortress 2 were the first games to add them.

As far as my research goes there is no indication there's an official date that they had timestamps added explicitly afterwards. Exposing the timestamps in the Steam community data xml feed was discussed in 2009 (forum was taken offline in 2017). One may assume that timestamps for achievements existed long before that as unlocked achievements were already displayed in daily summaries in the then available blotter feed.

UPDATE:

According to the data gathered during completionist.me development the earliest unlock date is 2008-09-11.