The oldest event I have is this.

2023-01-11 20:07:33.000 +0100

JB was likely the first app to support it, so maybe check release notes for Damus.

https://api.nostrgraph.net/beta/events/76772834388e8f8993cc247f8aeb7ebed4211663e804f368cbd499672559955d.json?pretty=true