The 'correct' answer is probably 'when you feel it's complete enough'.
I doubt very much that there's a hard and fast boundary.
I consider Dvoen and Maxna sketches as they only have notes reminding me of what features I wish to add, but I consider Iriex a conlang because it's begun the process of explaining how these features work.
I speak English and a touch of Gàidhlig.
I am creating a conworld, which I refer to as the Carrion Series
, that will contain three languages, Iriex