I'm not really sure if I'd want to tongue-kiss at all. I've only ever done closed-mouth kissing, and even that feels very strange to me (I enjoy being kissed on the cheek much more ). I tend to go back and forth as to whether I find tongue kissing to be appealing or not. If lip-kisses feel strange, I can't really imagine tongue-kissing to be all that pleasant. But like I said, I've never done it, so perhaps it does feel good?
Though if I was going to, I'd still wait until well after the third date, most likely. Love-shyness causes me to go at a very slow pace, so I'm always amazed at the idea of kissing on a third date.