First, we must assume that they can find Earth. They wont be able to simply calculate its position. Let's start with the assumption from this answer that we know the eccentricity of Earth's orbit around the sun to 8 significant figures. That implies our understanding of our position in space with respect to the sun may be off by 1,400m. We simply can't measure our position any more accurately than that, so that's the best we could write down. And that's just one source of error in one direction.
Having the time travelers observe the Earth before the day you do the teleport will help pin that down. Also it will help with another vicious issue: time tag errors. The Earth is rotating around the sun at roughly 30km/s. That means your 10m box in space is like a 300us box in time. If they aren't calibrating their process with respect to the earth, they're going to have a mighty short window where your box is actually where you say it is.
Since they're observing things and can move through time, I would make the box a "logical" box, based on geographic locations. There's plenty of time to survey the planet and get a good fix on our concept of latitude and longitude.
However, given that this is a story, there's some value in being flashy. We have a lot of events whose position in space and time is very well understood. For example, we know the precise position of nearly every nuclear bomb detonated because military engineers are sticklers for that kind of information. You can go find exactly where these events occurred.
More than seventy years after the test, residual radiation at the site is about ten times higher than normal background radiation in the area. The amount of radioactive exposure received during a one-hour visit to the site is about half of the total radiation exposure which a U.S. adult receives on an average day from natural and medical sources (Trinity)
And just for fun, I'd play games with the precise time tags, just because they amuse me.
Any time traveler should have been able to pinpoint the precise location of the first atomic bomb detonation. There would be no event quite like that in all of time. A great cusp in time and space where literally the entire world turned, and held still, all in one brief moment as future history was written.
Tom's disappearance was a much less momentous occasion. Pinpointing it in time from over a thousand years in the future required a bit more direct of an approach. Tom looked around to see if anyone was looking, and then swung a leg over the fence between himself and Trinity -- the true site of the first atomic explosion. He told himself "this is the moment," but he knew he was lying to himself. The moment was yet to come. None the less he breathed an audible sigh of relief when he found the device nestled in the rocks where only a fool would brave the radioactivity. Not that there was much radioactivity left, but there's just enough to help a time-traveler ensure nobody accidentally finds your clock before its time.
Tom opened the face of the device. The gleaming counter inside stared back out at him, counting 2,295,711,060 seconds upwards, with a fast moving blur of digits to the right. 2.3 billion seconds since world changed on that one night in 1945. Something about this felt fitting. Below the timer were two buttons: pause and cancel. One press of the pause button would anchor this moment in time, and his journey would begin.
Tom thumbed the pause button, closed the device, and threw it into the rocks a few feet away. This is the moment, he thought. In 10 seconds, the clock would fuse, indelibly marking that paused moment into its circuitry. If he were to sprint over to the rocks and clock the cancel button, the process would stop forevermore. This moment would vanish into history like so many moments before it.
Tom stood still. A glimmer of fear rippled through him. The cancel button was a nice failsafe, decreasing the likelihood of his actions rippling through time like the infamous butterfly flapping its wings. He could still reach out and keep time sane. But she was still waiting. "Is-has still waiting," he thought, remembering that time travel was going to require some new tenses.
Ten seconds later, the clock made the tiniest noise as it locked the time in forevermore. But Tom did not hear it. Ten seconds is a long time, but once that moment is anchored in time and space, it happens in an instant. The clock fused, and Tom vanished, all in one moment. And that was all.
Correction: that is-had been all.*
Bloody timeless tenses.