The phrase "a time when scientists" is correct and usable in written English.
You can use it to refer to a specific period in history or a situation involving scientists and their work or discoveries.
Example: "There was a time when scientists believed the Earth was flat, which has since been proven to be incorrect."
Alternatives: "an era in which scientists" or "a period when scientists".
It was also a time when scientists and engineers tended to be generalists -- educated and informed in other disciplines.
The national academies' report comes at a time when scientists are making spectacular progress in genome editing.
The announcement of cosmological expansion came at a time when scientists were beginning to grapple with the theoretical implications of the revolutions taking place in physics.
So Macfarlane's comments, coming as they did at a time when scientists are calling for smarter thinking about how we fund science, are unfortunate and unhelpful.
Working from the late 1970s to the early 1990s, Kish was active at a time when scientists first recognised and publicised global climate change.
There was a time when scientists who study human evolution had to content themselves with bone fragments and stone tools from our distant ancestors.
The Brontosaurus has been consigned to extinction not once, but twice – the second time when scientists concluded it was too similar to other long-necked dinosaurs to deserve its own genus.
Computer models predicted that the mercury would steadily go up as carbon poured into the sky, and pour it has – 40 billion tons a year, now; and two months ago the level of atmospheric CO2 crossed 400 parts per million (ppm) for the first time (when scientists began to measure it in 1958 it was 315ppm).
All this leaves little time for research, at precisely the time when scientists are called upon to make their marks as independent research scientists.
Au. sediba lived nearly 2 million years ago, about the time when scientists think the human lineage Homo originated.
Early recipients included Marie and Pierre Curie, Paul Dirac and Albert Einstein, who worked at a time when individual scientists could make breakthroughs in quantum physics and relativity.
