I can't really call it sci-fi because there is no science involved in the time travel although time travel theory does play an important part in the movie it's more about how true love can work miracles.
A sweet and pretty woman moves into an apartment complex one day she hears a voice from her air vent asking her to help save her neighbor's life.... the voice tells her he's from the future. At first, she doesn't believe it but eventually agrees to help. In doing so she ends up falling in love with her neighbor.
I gave it an 8/10. If you're in the mood for a "pure" love story this is a good one to watch.