I don't think there's a magic formula, or sure-fire timing in calling her back, or whatever. If you are interested in seeing her again, then make sure she knows that. Call her, remind her who you are, where you met, and tell her how much you'd really like to hang out sometime, or take her out, or whatever. I'd say give her a day or two, just in fairness to see if she returns your late night call. And if she doesn't call back in a day or two, call her back and be honest.