There is no time limit for your date (via iSnatch -> Take her out). You should give her the gift she is asking for (or better) and answer her quests according to her temper, then you will reach a point when the gauge/meter is not increasing. Of course you can continue answering her question, but this won't change your chances for getting her as fuck buddy. In fact you can leave the date screen and return/continue later.
The outcome of the date is random. So if you have a not fully filled gauge (needs for divine ones a 2 CC gift) the girl can deny your request and is gone.
