Daytime cocktail appropriate?

I have only ever attended black tie or formal weddings and I am not sure what to wear to an outdoor cocktail attire designated afternoon vineyard wedding this summer. This is something I already own so it would be convenient to wear again, however it is a little more full length on me at my height. Does this count as cocktail attire or does this read as more formal? Any alternative dress suggestions for this occasion / setting would be appreciated!