What purpose do the hills, railroad tracks, station, and precise time reference in the first paragraph serve?
The setting and reference to the hills that look like white elephants reinforce that the Jig is pregnant.
The lovers are sitting in the shade just outside the station. Beyond them is the light and tracks and baron landscape. As they sit in the shade, they begin discussing Jig having an abortion. In this way, they are trying to bring the issue into the light and get it out in the open. Yet, they never say the world abortion or really talk about her pregnancy directly. They are keeping it 'in the shade' - so to speak.
Their relationship does not seem one that will lead to anything permanent, which may well be the reason the American is pushing her to have the abortion. With this realization, Jig has a new perception of their relationship, one that is thrown into the harsh light of reality, like the tracks and baron landscape before them. The fact that the man does not want a child, which would make them a family, does this crush any illusions she might have about him and their future? Plus, without the child would she feel baron like the landscape?
The precise information about time at the end of the first paragraph reinforces the briefness of not only this story but also the couple's relationship. Like the train on its brief stop, we are offered only a brief moment in the lives of these characters. With the decision made, will the relationship be as brief as the train stop and our glimpse into their lives?