This is a rather underestimated time travel movie, based on trying to alter history by preventing the assassination of JFK.
It is notable for the era in that it spins quite an entertaining tale of the logical complications of doing so.
To my mind it hits just the right level of prominence for the technology involved, downplaying it somewhat, but offering just enough detail to give it some superficial credibility and more importantly, making it interesting to watch.

It really needs a DVD release.