OK so the opening and closing narration is as follows:
"Billions of years ago a race of immortals harnessed the most powerful force in existence: The emerald energy of willpower. These immortals, the Guardians Of The Universe built a world from where they could watch over all of existence: The planet Oa. They divided the universe into three thousand six hundred sectors. A ring powered by the energy of will was sent to every sector to select a recruit. In order to be chosen by the ring, it was said one must be without fear. Together, these three thousand six hundred recruits formed the intergalactic peacekeepers known as The Green Lantern Corps. Of all the threats the Corps ever faced, the gravest was an entity of fear known as Parallax. Only the legendary Green Lantern Abin Sur was capable of capturing and imprisoning this beast which he did on the lost planet of Ryut. Of all the Lanterns who have ever worn the ring, there was one whose light shined brightest. At first, his humanity was thought to be a weakness. And yet it proved to be his greatest strength."
So, when do we think this voice-over takes place? Obviously it's someone telling someone else the history of the Green Lantern Corps sometime after the events of the film. But when exactly?
Edit: Ok so according to the DC Wiki, Tomar-Re is the one telling this story. So that would place the story at least sometime after the events witnessed in the film itself. He's likely telling the story to a new Green Lantern recruit, similar to Hal Jordan and Aresia in "Green Lantern: Emerald Knights".
