I think the best time to kiss is when you are both comfortable...well if you can get to that point because she will be more then happy to give you a kiss.
I dated girl for 2 month's and we both liked each other.. Things went slowly as we couldn't get together alot.. About 2 times a week. But when I dcided to give her first kiss on a picnic, I just want it ti be an easy kiss, but she went for more than that... I was surprised and I didn't want to stop..