Very curious & unexpected ending.
Fact sheet.First published: Astounding, November 1948.
Among the stories from Astounding/Analog issues edited by John Campbell.
Related: Stories of John R Pierce.
Found a broken link? May be the story can still be found.
Trying to figure out science fiction
11:30 pm in this clock (that's 6 pm GMT).
The clock shows India time (IST). Note India doesn't have any concept of daylight saving time; so if your locale has it, the relative posting time will appear to have changed with your time change.