Any time an author manipulates time (flashback, slowing or speeding up time) it is to maximize the story line. Story = boy meets girl boy loses girl, boy wins girl back. Plot is how we take that story and make it heartrendingly real each time we tell it. Maximizing the plot means that the events are arranged to have the most impact. So, that may be a "bookend structure" (meaning starting at the end and then working back to that point. Or, it might be the opening events have happened and now it is a year later.
