The phrase "at a feast when" is correct and usable in written English.
It can be used to introduce a specific time or occasion during a feast or celebration.
Example: "At a feast when the sun set, the guests began to share their stories and laughter."
Alternatives: "during a banquet when" or "at a celebration when".
I saw the vigor of his majesty at every single feast when I was a child who could not yet conceive.
Nutritionist and host of The Cooking Channel's "Healthy Appetite" Ellie Krieger suggested making the most of seasonal vegetables at your Thanksgiving feast when she joined me on Mondays With Marlo.
Horror fans could pick up a copy of Blood Feast when they popped out for cigarettes or filled their car up at the garage.
"Stone monuments, grooved pottery, a particular type of arrowhead, a tendency at a drop of a hat to have a feast — and, when they're done, to drop everything in a pit.
Jungfrauenbecher were used at nuptial feasts when the bridegroom drank a toast out of the skirt cup and then was supposed to right the figure without spilling the wine in the pivoted bowl, which was to be drunk by the bride.
And it's in our DNA to feast when food is plentiful because at points throughout human history, famine was a genuine concern.
When Dante Alighieri and Beatrice Portinari were nine, they were introduced briefly at a feast.
But Eustace choked to death at a feast.
Spoons and knives were the chief utensils used at a feast during the middle ages.
By David Denby Jean Cocteau's "Orpheus," from 1950 (at Anthology Film Archives May 19-20), is a magical feast made at a time when magic was produced by nothing more than the malleability of the human body and by the (now peculiar) properties of the film medium, with its twenty-four shots shotakenken per second, which allowed directors to accelerate, slow, or reverse motion.
