I'm not a writer, but if I were this might have been a premise for a SciFi novel. It's not like I spend my days thinking about stuff like this, I don't need to, I'm an insomniac. OK, here's the setup, imagine some huge cyclical instability in the sun threatens life on earth, solar flare activity increasingly makes satellite communications difficult, at times getting bad enough to interfere with terrestrial broadcast signals. Where each of these things happen already they cease being an exception and start becoming a new norm. A scientific consensus forms predicting that coronal mass ejections are increasing in severity and frequency and will disrupt not only our communications networks but eventually our power grids. What's worse is that within three to five years the energy output of the sun will begin fluctuate rapidly but with a sharp downward trend. Within fifteen years the average temperature of our planet will drop up to ten degrees ushering in an ice age worse than any glacial period the human race has ever witnessed. It is estimated that between the loss of agricultural output and the disruptions that will almost certainly accompany these shortages, for every sixty people alive today perhaps fewer than one will survive the next twenty years. It is uncertain and perhaps unknowable if the sun will ever return to it's previous level of energy output.
Theories exist on how the sun might be rejuvenated but even if every scientific and engineering resource on the planet threw their combined weight on the problem no solution is considered even remotely likely. One thin forlorn hope does exist in some secret government lab, perhaps not a hope for those alive today but a hope that the human race it's self might survive. A time machine.
There are problems, the amount of energy needed to travel through time will almost certainly destroy the mechanism and when asked why if they can build one of these machines, why can't they build more the scientists involved look a little sheepish but insist that the aliens at area 51 never existed so could never have given them the device. Normally such a statement would have caused an uproar but under the circumstances even Art Bell was quoted as saying "who cares where it came from, where the hell should we send it"?
As it turns out the device functions as follows. The "launch platform" is 100 feet by 100 feet square and the displacement field extends 100 feet above it. So in the process of sending a 100 by 100 by 100 foot cube to any place on the planet arriving at any point of time, the device melts it's self into useless glass and metal, but the cube will arrive at the selected place and time safely and intact.
Which brings us to the big questions, what do you fill that cube with and where/when do you send it to? Do you fill it with scientists, engineers and supercomputers and go back 40 years and try to fix the sun, or do you go farther back in time with a much different payload and different objectives?