There's always a risk of rejection involved whenever we reveal problems or difficulties. In my experience, there have been far better outcomes when I get past the first stage of politeness and onto showing the real me and getting to know the other person in the same way as soon as possible. So I'd say the time to bring it up is sooner rather than later, but not necessarily the very first time you hang out. Maybe the second or third time though, if you feel like there's the possibility the relationship might turn into something special.