Yeah, my first reaction to this is something along the lines of the idea that exactly when this happened (and exactly how it’s defined) doesn’t seem as important as the broader recognition that this is a thing.

The impacts of mega-scale human activity do naturally vary from place to place, and it makes sense that the “exact start” would understandably vary from place to place, along with how well-defined it is in stratigraphic and other records. But the more important recognition is that, to reference a famous quote, “we’re not in Kansas anymore”. We’re in uncharted territory as far as our understanding and predictions of the Earth system go.

If this celebratory marker-placing draws more attention to the matter – which I’d say it certainly seems to – then I guess it’s a good thing. But the specificity of the marker is more of a matter of trivia or (preferably) a conversation piece to make the point about the sheer scale of anthropogenic changes to our home planet.