Assuming the multiverse theory is real, how would time work with the alternate versions of ourselves?

If you take a point in OUR space to be represented by x,y,z,t
then with the multiverse it might be represented by x,y,z,t, Q
If there are an infinite number of multiverses then the only limit is your imagination.
OK so in one of them your parents met in school, had an affair and an illegitimate child. In 1975.
Why would you imagine that this is a version of YOU?
YOU weren't born THEN in this universe only.
If a new universe is spawned every time any decision is made by anything at any time in the past then there is absolutely no limit to what MIGHT exist in any of these other multiverses.

So to assume that this is "real" is a big ask.

WHY, why , why do these other universes HAVE TO HAVE THE SAME LAWS OF PHYSICS , thermodynamics and quantum mechanics as THIS universe has. WHY do you ASSUME that there are MULTIPLE "you's in those universe's. What if EVERY imaginary universe you create in your imagination BECOMES reality, but the laws of physics, including TIME ARE DIFFERENT./ You KNOW what I mean. The universes where you can fly and have any super power you want.. MOST of us have fantasy lives of some type., but if we CANNOT tell the difference between the Reality" of THIS Universe" and our make believe , fictional universes, THEN you have a serious problem.

No , The laws of physics , including TIME, DO NOT HAVE to be the same. YOUR PERCEPTION of how fast or slowly time is passing IN THIS UNIVERSE depends on your metabolic rate, how fast the chemical reactions are taking place and how fast your nervous system is transmitting the electrical signals to and from your brain and how fast the neurons are transmitting./ Time really DOES flow faster FOR YOU when you are having fun, and that INCLUDES MENTAL activity.like using your imagination.

HOW do YOUR actions in those OTHER universes, IF they exist, impact YOUR life in THIS Universe? NOT AT ALL. You have a brain and a free will. if you do NOT USE AND EXERCISE your BRAIN, you "lose" It and your mind becomes "closed" because you DO NOT exercise it. Whether the OTHER universes exist or NOT is IRRELEVANT to THIS Universe..

What about the universes whee JFK WAS NOT assassinated. Or Lincoln, or the south won the Civil war. Alternative history fiction is a thiving genre of fiction for the last !) YEARS OR MORE. I recommend anything with Eric Flint or harry Turtle dove. The South DID win the Civil war in some Harry Turtledoves books.

Maybe you should read Robert A. Heinlein's "The Number of the Beast" which was his Swan song, his lost published book, but Heinlein is lot to take on if you have never read him. you really should read something published BEFORE "Stranger in Strange Land.. " Heinlein was a rear admiral during World War 2.

If you are referring to the Many Worlds Interpretation of quantum mechanics, that is not how it works. Each possible state of a quantum system occurs. That has a very precise mathematical meaning. It does not say that there are trillions of universes, each slightly different. That is science fiction.