Time only exists as the universe exists. Time is part of the fabric of the universe itself. That's why it's called space-time or the space-time continuum.

So, there was no time before the universe began. And, yes, the universe did have a beginning. It's called the Big Bang. It's how all universes begin.

Also, time is not constant. Einstein's theory of relativity explains all this. But, that gets too weird for me trying to help you understand what I wrote.

There is an arrow to time. Thus, we cannot go backwards in time to change historical landmarks, for example. Since we cannot go back in time, then, shows that purport to go back in time to fix the past to correct the present are a fiction, then.

I hope my little discussion on time helps you.

Peace.