It would be just a quarter of three
preposition
10 North American Expressing time in New Yorkrelation to the following hour.
'it would be just a quarter of three in New York'
(formfrom Lexico here)
What is "it"? 2:15 or 2:45? Lexico simply says that in this sense, 'of' "expresses time in relation to the following hour" without elaborating on this.