Its a moot point until FTL, anyhow. Imagine if you will...
You fall off your toilet and bump your head. Suddenly, you have the idea how to step outside of spacetime and re-enter in the past or future. Its the Fluxored Capacitor! So you set about creating it and installing it in a 2008 Dodge Charger. What, a Delorean? Thats so 80's.
Anyhow, you climb into your time machine and set the clock back ten minutes ago. You step on the accelerator and get up to 88 MPH and....
You die in the vaccuum of space.
Because, even though you did manage to go back in time, you forgot that the earth is constantly moving in space. When you went back in time ten minutes, you ended up in space where the earth will be ten minutes later.
And so, as you choke on the last rivlets of blood that are boiling out of your tongue, the earth catches up to you and you burn up on reentry. Scientists spend the next hundred years trying to figure out how a Dodge ended up crashing through the roof of a home in Schenectety.
(a comment at Q and O)