It is not incorrect. But you can make it even more clear by specifying what exactly you mean. There can be 2 aspects of looking at the above text. First, if you're asking the person when is he going to visit you. And second, when is the person going to visit some place where you both probably had been to before. If it's the first case, you could say: When will I
Yes it can be written that way as well but then again, "when do we visit next time?" is situation specific. It cannot be used in general. And as for "When will you visit next time?", this is also correct.