Visiting hours, naturally, had to be based on local - Earthside - time, but it was no help to anyone when those who came were confronted with a series of inert lumps, even if those lumps were fifty lightyears from home.
Attempts were consequently always made to adapt the aliens to a twenty-four-hour day. Some adjusted easily; others could not at any price, being too tightly fixated on their home world's night-day cycle.
During the ten hours of the day when the zoo was open for visitors, as many as half the exhibits might be slumbrously dull. Alternatively, the cycles might chime together and the whole place become a buzz of vigorous movement, colour and sound. The latter occasions always brought visitors in hordes because they were always well advertised. for convenience they had to have a name and a definition: a Coincidence Day was one where forty or more of the fifty presentations were at day activity peak for at least five hours.

A book of science fiction short stories first published in 1968. My favourite was "Coincidence Day" which was about a zoo of extraterrestrial species on Earth. I also liked "A Better Mousetrap", "Seizure" and "Treason is a Two-edged Sword", but overall I prefer this author's novels to his short stories. ( )

Lots of charming short stories - amazingly sweet Science Fiction.

Martians get word of the first manned trip to Mars and assume they are being invaded. What to do? Well clearly they should teleport the Invader there early and deal with the Terrible Threat. Unfortunately they get his dog Jeff instead who mistakes them for cheese flavoured mice.

The N.A.S.E.E.Z. Zoo is accused of mistreating 'dumb animals' and is nearly exposed for what it really is - an exchange program for aliens on study tours