It can take a very long time; months even, for her pain to be gone. Continue being the caring man you seem to be, and you'll do fine. Just remember to get her very stimulated before hand, go slow, and use lube if you need to!

It should not take any amount of time since there should never be pain to begin with. Pain is a sign that something is not going right. So many people wrongly assume that women are supposed to feel pain their first time, that their hymen is breaking and causing them pain, and that they are too tight which is causing them pain. None of that is usually the case, however.

The number one cause of pain during sex, first time or otherwise, is lack of lubrication. That's easy to fix. You can make sure she is lubricated or buy some at the store.

The second most common reason is being tense. The vagina is very stretchy, first time or otherwise, when a woman is relaxed and in the mood. The vagina easily take on the average penis even if it is the girl's first time, even if she does not use tampons, and even if she does not use penetration to masturbate. Many girls tense up their first time or first few times, however. That can make the vagina pretty much clamp shut just like any muscles in your body tighten up when you're nervous. Sometimes this happens without the girl even realizing it. Sometimes it happens more out of excitement than being nervous, so it doesn't necessarily mean that the girl isn't ready or that she is uncomfortable with the guy.

The third reason and least common reason is various problems such as infections which she would have to see an ob-gyn for.

Many women feel pain their first time or their first few times, but in most cases that pain could be avoided if only the people knew more about the human body beforehand. Try to make sure she is relaxed and in the mood. Buy lubrication if you need to. If the pain persists, urge her to tell her ob-gyn about it. Girls are supposed to see an ob-gyn when they become sexually active anyway, even if they do not have pain or any other problems. So that is something she should do soon either way if she hasn't already.

I have a friend who's pubic bone is actually facing the opposite way of what most women's do. She was experiencing pain during sex for the longest time, and finally her gynocologist (sp.?) discovered that her pubic bone was backwards...Your gf might want to go to the doctor just to make sure it's nothing like that.

P.S. Even if it is something like that, there are certain positions you can use to minimize pain and maximize pleasure. Good luck!