If it existed at any point in the next million years someone would have already come back at some point in history. You may say they have strict regulations against exposing themselves to us. However say that it was created in the year 4000 if it existed for all time after that then someone at some point with access to time travel clearance would have gone crazy or depressed and likely said -blam!- regulations and gone back and done something stupid in order to purposefully reveal their existence and show proof by telling people what will happen on a given date. Edit: this is also not including the obvious science to why we couldn't bend time/space without pretty much destroying the planet lol.