You can easily cross calculate between various, inertial frames of reference. The problem is that earth isn't sitting still in an inertial frame. We spin around the sun, and we orbit the center of our galaxy. We also get nudged about by the pull of other stars.

Tracking a time jump (or technically a time-space jump) would be easy, if you just wanted to be within the solar system. With measurements the earth-moon gap would not be too hard. Hitting a surface exactly would be another story. Miss by a meter and your cut in half by a wall or floor.

You know what they say: the best time to build a time machine is 50 years ago.

I think that's basically the movie Primer too, they'd turn the machine on, go hide in an apartment for X amount of time, then go back to the machine and emerge 5 minutes after they turned it on and just walked away.

But gravity effects time, sticking close to a planet isn't going to be hard.

Ironically enough the first (if we ever get them) time machines are going to be a hell of a lot like modern "UFOs" are described. You couldn't risk landing on the planet, elevation changes are what's really a nightmare to account for. Show up and hour early and everything is a foot higher because of how fast we're spinning.

So you'd want a space craft, because space is big and empty. And realistically it's going to take something bigger than a telephone booth or even the 1980s embodiment of Florida on four wheels with a hood designed to do cocaine off of to house a time machine.

Damn physic laws removing the fun from physics

Basically half the plot of quantum break