Still, as in all time travel films, the plot starts to unravel if you think too much about it. Bristol deals with some of the issues by imposing specific constraints: CJ and Sebastian’s device only allows them to go back a week at the very most, and their time/space continuum wormhole closes after 10 minutes. This gives the characters a deadline (technically, CJ and Sebastian only have a finite window of time to save Calvin — once they get past the one week mark, they won’t have enough power to return to that moment in time), but the ticking clock comes off as artificial, mainly because many of the setbacks they face seem like they could easily be solved with small tweaks, like jumping back from a different location, or approaching a conversation just a tad more diplomatically.