LOL im a bit late posting here all i wanted to double check where the term came from as i like to know random facts lol.
I'm fully English with generations of English behind me and i have always used o'clock and I don't think its dying at all, all my kids and their mates etc use it its very common here still but when abbreviating anything it will often get missed but for example i list a few things that i or all others i know could say when talking about time.

What's the time?

Twenty five to nine.

Oh, when's the film starting?

Ten.

A. So if it's starting at ten o'clock why ain't we leaving 'till half nine? But if we leave at quarter past we'll make it in better time to get food etc.

B. Ok mate we'll do that then we'll probably be back by about Two a.m to be fair.

A. Yeah then bed by three, and up again at 10 in the morning as i have a one p.m meeting.

B. Fair dues well we'll relax for a bit then get ready at five past.

A. Yeah sounds good.

That would be a normal conversation in person but uses multiple different forms. Obviously the term o'clock isn't used much when texting as we all know that everything is abbrieviated in text messaging eg
If i tld u wot time it was it b bout 6pm giv or take a few mins but in 15 itl be bout 615

Either way i just say what ever seems right at the time place and even who you are speaking to whether formal or in formal.
That aside i do listen and watch an awful lot of American produced music and movies and i have never heard the term 'a quarter of' most of the time all i hear is quarter to but the difference i have picked up on is that they often say both numbers more often then reference to minutes past as a metric value like quarter to or past and half,
e.g at 10:30am A typical common english person would say
"Its half ten" Where as an American would say "it's ten thirty".
I am not saying that ALL American and ALL English say it exactly like that as i know both in America and the UK the local language differs extremely, even people that live a few miles further from London (My area) have completely different slang words and terms that they commonly use but i am going by what i here most.

Back on subject the term 'of the' sounds right but i wouldn't say that the term "on the" is wrong either, as that is still used when people say things like on the dot and on time. And there were massive differences in older english times speaking capabilities and languages used as there was such a separation in class from hard working low paid peasants to stuck up lordy lazy royals and other wealthy families.

But the comment about the Irish term O' meaning son of isn't only Irish it was also Scottish along with surnames with the word "son" on the end or even the word "kin" But that has nothing to do with time telling.

A lot of interesting references to other languages seems right too as the way we all speak has been changing and adapting for thousands of years and every area in every City, County, State and country etc all have their own twist on it

Thank you all who posted it was interesting lol