This slasher-thriller begins promisingly, following the familiar "time loop" movie rules, but it eventually devolves, finally feeling like little more than an unsatisfying gimmick. 6:45 has the interesting idea of focusing on a couple, rather than just a single person, but the filmmakers don't seem to have put much thought into just how Bobby -- the one who's stuck in the time loop -- would try to communicate with his partner, Jules. He just seems to mope around and get mad, pretending to go through the motions of the day. (Perhaps a better idea would have been for the couple to be stuck together, as in the much cleverer, more touching Palm Springs.)
As the movie goes on, Bobby becomes less and less likable, and he never seems to use the time loop for anything positive. One day, spent entirely indoors, might have had some charm, but it's punctuated by angst and then a silly character mistake. Perhaps most frustrating is the fact that Bobby can never seem to escape the masked slasher. The killer just walks up to the couple and does his stuff, and Bobby stands there, slack-jawed, while the killings happen again and again. When the final act comes, 6:45 tries for a "twist," but the nature of the twist negates the entire idea of a time loop, and it feels like we've been swindled.