It varies. Some evals a 1,2,3 days long, but those are usually highly structured, formal evals, often done by a neuropsycholgist. Some evals are rather "informal" like mine. I was "informally" dx'd over the course of being treated for depression, where I met regularly with a psychologist and psychotherapist, seperately, to determine what, if any, other conidition may be an underlying factor to my chronic depression. Over a few months, I was evaluated for other possible conditions, but those were ruled out. I actually brought up the possibilty of AS myself, but it was several weeks before both the psychologist and therapist felt like they understood what I was experiencing well enough to say it could be AS.