Most Helpful Girl
You should ask them out before you get put in the friendzone, but not too early on as to creep them out. Maybe wait a week, and if she seems interested then go for it!
Most Helpful Guy
There's no such thing as too early. If I like a woman, I'll ask her for her phone number the same day I meet her. You don't want to give her any opportunity to put you in the "friend zone." She needs to know that you're a guy who knows what he wants and goes for it.