Daniel sets a timer on his phone and holds Natasha's hands. Natasha thinks about what she knows about eyes, and Daniel tries to come up with the words to describe Natasha's eyes. Natasha relives her day while Daniel wonders if they'll meet again. In the last minute, they think about the hurt they're going to experience. When the timer goes off, they promise to keep in touch, but they know they probably won't. Natasha suspects that "meant to be" doesn't always mean "forever." They understand that love can change everything.
Even though Natasha and Daniel don't necessarily mean to keep their promises to stay in touch, making the promises now allows them to exist for a little longer within the confines of their intimate relationship. Further, and most importantly, they've both now learned that intimate relationships like the one they share are the most important things they can possibly strive for in life.