For good or bad, everything unfolds purposefully. Because of one miniscule prank these two young lovers' lives may well be changed forever. Before taking the 'morphine' it seemed they were parting ways. Now, with the help of the prankster, their bond is stronger than ever. The Butterfly effect, if you will.
Another thing that struck me at the beginning was the periodic table underneath the backwards clock. My interpretation: As time counts down, the more the little things matter. A simple visit to my grandparents' place last week is a great example. They were thrilled. I am going to start seeing them more.
Or maybe I'm reading too much into this?