Not at all. There is many ways to rationalize time, nothing is settled at all. The “settled theory” you talk about would create paradoxes, if time travel is ever made real. And paradoxes don’t work well with reality.

There is actually a fairly common way to rationalize time that is the opposite of what you’re describing: Time is entirely a construct, there is no past, no future, only the present. Take away all of humanity’s memories and the last doesn’t exist at all.

There’s also an understanding of time that says it only goes forward, making time travelling to the past impossible.