The phrase "a time when establishment" is correct and usable in written English.
It can be used to refer to a specific period or moment in which an establishment or institution was formed or became significant.
Example: "The 1960s marked a time when establishment figures began to lose influence over the younger generation."
Alternatives: "an era when establishment" or "a period when establishment".
But it's probably not a terribly helpful argument to make at a time when Republican establishment types are openly talking about wresting the GOP nomination from Donald Trump at the convention.
His decision to endorse Trump at a time when the establishment of the party was still very focused on beating the real estate mogul turned Christie into persona non grata with lots of his old friends.
Activists have exceptional moral sensitivity; they become aware of the immorality of some social practice at a time when the establishment considers these practices unproblematic.
Mr. Brinsley's Instagram posting shortly before his death, in which he vowed to put "wings on pigs," recalled a frequent refrain of the Black Panther Party, "Off the pigs," in the late 1960s, a time when anti-establishment sentiment spilled into violence against the police.
At a time when few establishments welcomed openly homosexual people, the Stonewall Inn in the 1960s was known to cater to a wide array of gay patrons.
The candidate herself seems more aware of the dangers of appearing part of the establishment at a time when an anti-establishment mood appears to be prevailing.
This was a time when the architectural establishment venerated formal training, particularly at the Ecole des Beaux-Arts.
He is still dividing the country and there are still disputes over the extent to which his output in the last few years of his life confirmed him as a great radical thinker at a time when the British establishment was trying to crush all vestiges of the movement for political reform.
Foot was editor of Tribune twice, and at a time when the British establishment sought appeasement with Nazi Germany, Foot's Tribune was first to bellow "Hitler means war!" But then, this was the weekly that championed the International Brigades in Spain and denounced Rothermere's Daily Mail and its sympathies for Oswald Mosley (expressed in that seminal headline "Hurrah for the Blackshirts!").
She was fascinated by subcultures at a time when the art establishment wouldn't touch them.
