You are not obliged to disclose autism (PDD, Asperger's, or whatever) anytime, neither at the start of the conversation nor after 2 hours. Even if you interact with friends, you are not obliged. Disclosing AS or not disclosing it, should be based on free choice.
If there is no stigma, you can tell something about it, in the same way to openly talk about other things. But unfortunately there is a stigma, and therefore I will be reluctant and cautious about it.