Wiktionary
quarter of
n. (lb en US idiomatic) quarter to, fifteen minutes before the next hour
Usage examples of "quarter of".
A streak of yellow light slashed out of the east, and at its tip a fireball exploded, scattering trails of luminance across a quarter of the welkin.
Northward, in the quarter of the fireworkers, there was a vast glare on the underside of a pall of smoke, suggesting that all the stored fuel had been set ablaze at once.
That gives us exactly a quarter of an hour in which the crime must have been committed.
With the door only a quarter of the way open, it ground to a halt and refused to go further.