You can enter symptoms in the first question, and then move on to the second question. At this point, regardless of the timing selected, some of the symptoms drop off.
In my case, at the end, "What are my chances of having..." reported 0% for the correct diagnosis. This is not good.
What is worse: the condition is in your database and described perfectly there, including the details that would allow for a correct diagnosis.
Did you try starting from each condition, and measuring how often you get the diagnosis right? Correcting for the prevalence of each condition as needed - in my case its a common one so there didn't seem to by any reason not to get it right.
Also, it would be nice if the conditions page would tell you how often this condition happens (if needed by asking age group/sex).