it depends, how much do you know about eachother?
if you know alot about eachother IE: age, address, how many pets you have, etc.
then go for it man!
but if you dont know alot about eachother, then wait a week or two then go for it!
give it a go!
^virgins
if you wait too long, she'll lost interest, the relationship you have will lose its edge, etc.
tru dat
you better ask her out soon, but not TOO soon
and don't go "do you want to be my girlfriend" unless you're 12, ask her to lunch or something, a movie would be good also