If this truly is an Apple watch event, it has peculiar timing. It's at least a full month before it's release. Either it's something else (iPad Pro, MBA) or they have some significant new features that would require such a time lag. Maybe something for developers??
Remember for iPad/iPhone they always have the event a week and a half before release. And for the iPhone/iPad initial launch sure they announced months in advance, but I don't believe they had another whole media event dedicated to announce it's launch/further details...
For the gen one iPhone and iPad, there was a final announcement about a month before they went on sale, detailing date and final price and specs.