When is the right time to mention about your stutter to a unknown person?

When is the right time to mention about your stutter to a unknown person? Guys, when is the right time to let an unknown girl know that you are a person who stutters? When trying to approach girls in places like in public, gym, train, or at the bar when you think there has been enough eye contact to make a move, is it better to start off by letting her know you stutter or let her know of it after you get to know her? I personally feel that I should let them know before, so that I will not lose my speech in between and that would make me look like a fool in the very first meet. How do you guys start off in that situation?