I read this short story during the late 1980s to early 1990s in an english language collection.
This story involved an art thief asked by some mysterious clients to acquire a priceless piece of art that was on display in a high security art gallery. When the thief suggests it is impossible, he is given a device which significantly slows down time, allowing him to walk in and take the picture off of the wall in the middle of the day.
The story ends with the art thief handing over the artwork to his clients, and asking if he can keep the device. The clients humorously explain that he can keep the device for the rest of his life, explaining that they are aliens collecting significant human works of art so as to preserve them from the impending human apocalypse.
When he asks when the apocalypse will occur, the aliens tell him "moments away in real time", leaving him the option of living out the rest of his life in slowed down time alone.