As for the actual time travel, I had always assumed that the Man of Steel time traveled as he always did, via high speed, but in the extended edition of the movie, Donner states: “And he stops the world. And now it’s actually going backwards. Which means, none of this actually happens.” Is that right? Does he reverse the spin of the Earth? CJ Moseley has more to say on the matter over at the Time Travel Nexus.
Apparently, people in early 20th-century Cambridge espouse many wise thoughts about time, parallel universes that encompass every possible combination of events again and again, and something about every decision every made creating a branch point. In the end, it's difficult to make a cohesive model of time from the plotline of Dimensions, but we tried our best to do so in our plot notes.
Handy Hint: The movie is eminently more watchable in a late-night group where everyone shouts “Great Scott!” whenever a character spews a sequence of pseudoscientific quantum mumbo jumbo that vaguely resembles an English sentence.