Related to your already-off-topic War of Prepositions, I’ve always been annoyed by the British usage of the word “of” when telling the time. “What time is it, mate?” “It’s fifteen of three.” WTH, people? I can make out that fifteen refers to minutes, but “of” doesn’t tell me if that means fifteen minutes TO three, or fifteen minutes AFTER three.
“Of” makes this a directionless vector, meaningless in this context. As Churchill [never] said in reference to ending a sentence with a preposition, “[this is] offensive impertinence, up with which I will not put.”
The only plausible explanation I can invent is that it may be an extremely lazy contraction of the word “after”.