Journey to the Center of Time

Journey to the Center of Time is a 1967 U.S. science fiction film, directed by David L. Hewitt, and starring Scott Brady and Anthony Eisley. It is a remake of The Time Travelers 1964, and was also known as Time Warp.

Meanwhile, as the scientists leave the cave, Gordon stumbles and falls to his death in molten lava. Mark and Karen find the time machine gone then it mysteriously reappears. They board it and return to the past, but arrive the day before their initial departure as a result, they find themselves in a parallel dimension, witnessing their past selves living at a much slower time rate. Knowing that the simultaneous presence of their past and current selves in the same timeline could fatally disrupt the timespace continuum, Mark and Karen hasten back to the time machine to rectify the problem, ending up hopelessly lost in time and space. In the final scene, the machine, with the two scientists onboard, is shown drifting among the stars towards an unknown fate.

Source: Wikipedia