I just remember this one bit of this book: the idea that the protagonists jumped from world to world in a set of parallel universes but, because of the world's differences, it looked like time travel: one might go from an Earth post-WWII to an Earth pre-WWII... but it wasn't time travel.
This was the idea behind Andre Norton's The Crossroads of Time (1956). It's about a man in our Earth - Blake Walker - who gets mixed up in a hunt for a criminal from a different Earth and travels through several different Earths throughout the book.
That's one of the conceits of Michael Crichton's Timeline (1999); they aren't actually traveling in time, but rather jumping sideways into parallel Earths that are very similar to our world, but slightly ahead or behind in the timeline.
I'm not sure why parallel world hopping is supposed to be less ridiculous than time travel, though, to be honest.