A picture of my wardrobe circa 2013. It has more than doubled in size since then!
Personally, I find mine to be somewhere between those last two--enough items to wear a Lolita coordinate for about two weeks without repeating a dress/main item, and when you don't feel any need to buy any more dresses/have completed your wish list. And according to that self-definition, I still have quite a ways to go. My wish list still has quite a few dresses I want to track down or make on it.
But I can't imagine that I'll ever entirely "complete" my Lolita closet. I think that there will always be something on my wishlist to buy--some print that just came out that I can't live without, some basic that either got worn out or I never purchased in the first place (*cough*underskirts*cough*). So I don't know if I'll ever be able to consider my wardrobe truly "complete".
If the question is hinting more at when I had built up a wardrobe with enough clothes to do a few different outfits, had all my basics, and so on--then I'd say it took me around six to eight months. By the end of that time, I had a small collection of blouses and JSKs, as well as a few different accessories to mix together to form different outfits. But even then, I don't think that it was quite "complete" by my standards!
So I guess the tl;dr is that it took me about six months to get to the point where I had a workable wardrobe, but I don't think that I'll have a truly "complete" wardrobe for quite a while yet, even though I've been in the fashion for about three and a half years now!
The post above was a response to the Lolita 52 Week Challenge made by the ever so delightful Caro over at FYeahLolita.