I usually upload them once I have an idea of who they are, even if their profile isn't 100% complete, and make them private until I get at least one drawing of them, aka the reference. As a writer, it's way easier to come up with a personality and story than a design, so if I'm designing them myself, I prefer to develop them first so that I won't end up changing their outfit or color palette once I've started, since I'm not that good at drawing and really dislike having to redo things. If the design is an adopt or a custom I got from someone, I upload them as soon as I get the art reference and develop them later, once I've decided what story would fit them better (if I hadn't thought about that beforehand, that is).