When writers typically convey their stories of time traveling devices and the resulting adventures, they rarely take into consideration the true space-time continuum and where one might actually end up when they travel faster or slower (or even in reverse) relative to that which we are accustomed.
The Earth rotates on its axis, orbits the sun and follows the general swirling path of the arms of the Milky Way galaxy. How fast does the Earth spin? It takes a 24-hour day to rotate one time on it axis and the Earth is about 24,900 miles around it's equator, so...The Earth is spinning at just over 1000 miles per hour! That is roughly 500 yards (or the length of five football fields) per second!
What's my point? Well, if you went back in time ONE HOUR, you would be over 1000 MILES away from the point where you started! (The Earth is not a perfect sphere. One could end up inside a mountain, in the ocean, or falling through the atmosphere!
) And that is only taking into consideration the SPIN of the planet. What about it's orbit around the sun?
The Earth travels about 585 MILLION miles each year around the sun before returning to it's relative starting point. If you went back (or forward) in time by one month, the Earth will have moved almost 50 MILLION miles from where it was.
In short, if you set your time machine to travel somewhere in time, you better be prepared to end up somewhere in deep space or, less likely but even more hazardous, showing up in side of some planet, asteroid or star (which would be EXTREMELY bad for the time traveler).
And THAT does not take into consideration the motion of the Earth and the Sun and all the rest of the stars and planets in the spiral arm of the galaxy.
So, if you are writing about time travel, consider ALL the factors involved.