Eastern Daylight Time on April 1, 2018 with a window of plus or minus 7 hours. In the continental US, that's Sunday evening.
Its re-entry into the atmosphere, therefore, will not be controlled and according to the latest calculations, it could occur between the latitudes of 43 degrees north and 43 degrees south, which includes a large part of the planet.
The chances of Tiangong-1's re-entry are slightly higher in New Zealand, Tasmania, the northern states of the U.S., northern China, the Middle East, central Italy, northern Spain, and parts of South America and southern Africa.
"The date, time and geographic footprint of the re-entry can only be predicted with large uncertainties".
It's not an April Fools' Day joke.
The 10.4-metre-long (34.1-foot) Tiangong-1, or "Heavenly Palace 1", was launched in 2011 to carry out docking and orbit experiments as part of China's ambitious space programme, which aims to place a permanent station in orbit by 2023.
One of those missions included China's first woman astronaut.
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China sent another lab into orbit, the Tiangong-2, in September 2016 and is a stepping stone to its goal of having a crewed space station by 2022.
Dr Jonathan McDowell, an astronomer at the Harvard-Smithsonian Centre for Astrophysics, estimates that Tiangong-1 is the 50th most massive uncontrolled re-entry of an object since 1957, when the Soviet Union launched Sputnik 1 - the world's first artificial satellite.
Because we have no telemetry from the station, we only know what we can observe from outside the station (like Fraunhofer's radar imagery, shown above), and a host of variables make it hard to say anything with certainty.
" 'It's just not a very likely event that a particular person would have a problem with it, ' he says. And one hour still means nearly one revolution around the Earth", said Holger Krag, the head of Esa's space debris office.
Markus Dolensky, technical director of the International Center for Radio Astronomy Research in Australia, said witnesses to the Tiangong-1 descent should see "series of fireballs" streaking across the sky - provided there were no clouds.