the general consensus with girls i know is this
when hooking up, most girls i know are willing to go so far as a blowjob, as long as they are returning the favor.
when in a relationship, it usually takes them about a month until they're comfortable with that, even if you go crazy on them.
maybe girls i know are just weird but i think thats kinda off haha. i'm pretty sure they just want a solid amount of time in the relationship before getting down and dirty so that the relationship doesn't become all about sex, which sort of makes sense.