Time is the 4th dimension. Not a figure of speech! It is the next direction after up, down, left, right, back and fourth. You cannot see it or point to it because atoms are only 3d. Light waves bounce off 3d atoms and reach your 3d eyes. There is nothing to look at in the 4th dimension.
The universe is expanding in the 4th dimension at the speed of light…. it is expanding through time. I am a big old-school Doctor Who fan and the idea of time travel is so much fun to think about…. but I’m afraid it’s just not going to happen. You see…. nothing exists outside of the time we are in right now. All the atoms in the universe are riding the cosmic wave front. The past is when the universe was smaller but it will never be smaller again. You cannot travel back in time because no atoms exist there.
Now one thing I have considered is alternate time lines. Ripples in a pond are always followed by more ripples. There could be entirely different timelines tagging along right behind us. But if that was true and you could travel there somehow, the place you end up in would be nothing like the place you came from. It would be an entirely new set of cause and effect reality. It may have started out very similar to our reality back 13+ billion years ago but there would be nothing to keep these different realities the same and even the slightest difference 13 billion years ago would change quite literally everything about that universe.