But sometimes a preposition isn't always a preposition.  Sometimes it's a verb.  In the above sentence, wouldn't "is from" be a verb phrase?

Well, thank you, Nadir.  Grammar isn't my strong point...but I still try!

Yes, but I think this is a case where common usage would take precedence over correctness!  If you said 12 am, but really meant 12 noon...people would think you were confused or just made a simple mistake!  

One often sees confusion or feels confusion on this issue of how to label midday.

Yes, but it's quite surprising--and even more disappointing--to see such confusion propagated in CathInfo, where readers should be able to expect that members whose postings are intended as corrections would refer to Latin, the sacred language of Roman Catholicism, when appropriate.  As it is herein.

My reasoning tells me that 12 noon is one hour after 11 am and so should called 12am, but to be correct and avoid confusion I would say 12 am or   12 noon.

It doesn't become pm or afternoon untill   after 12 am .  12.01 pm is one minute after 12 am or   noon.

ArrrGH!  NoooOOOOOO!

Noon is exactly "MERĪDIĒ" (m. ablative-of-time), contracted from "MEDIŌ DIĒ", meaning "midday",  and properly abbreviated as "M."--no "A." and no "P."!   Awareness of this set the explicit U.S. federal standard until recently [†].

The familiar "A." abbreviates the Latin preposition "ANTE", meaning "before"; the familiar "P." abbreviates the Latin preposition "POST", meaning "after" (each preposition taking the accusative case).  Is it really necessary for me to point out that in any natural reckoning of time,  "noon" is neither "before noon", nor "after noon"?

I think this is a case where common usage would take precedence over correctness!  If you said 12 am, but really meant 12 noon ... people would think you were confused or just made a simple mistake! 

A fine example of nonsense in defense of ignorance and ambiguity!  That which is correct can be looked up in a credible prescriptive reference source.  Whereas whatever are the most common usages of the moment can't always be--perhaps to avoid propagating ignorance--and may change with each arriving generation.  Maintaining & using that which is correct is the simplest way toward preventing or eliminating confusion when attempting to convey thoughts or ideas accurately.

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Note †: The change away from straightforward Latin would fit the overt hostility to Western Civilization for which the Obama Administration was notorious (less so the Clinton Administration).

Yes, but I think this is a case where common usage would take precedence over correctness!  If you said 12 am, but really meant 12 noon...people would think you were confused or just made a simple mistake!  

Common usage can be correct or incorrect.
That's like saying "everybody does does it so it must be OK". I know you wouldn't say that to your children, when it comes to doing wrong. Not that this is a moral issue. But it is always better to clear/correct in what you say than to be unclear/incorrect.

Some pet peeves of mine. 

• When people say bias when they mean biased. Bias is the noun, biased is the adjective. "The referee is biased" not bias.
• When people say "I could care less". That means you do care, and does not specify at all how little or how much you care. It's "I couldn't care less". This issue seems to be mainly an American one for some reason, over here everyone says couldn't.
• Another American one. "I got done". No, no, you finished. You did it. You don't *get* done.

I am pleased to see you are correcting me. Thank you, Alligator for clarifying and correcting. I see now that 00.00 and 12.00 are neither a.m. nor p.m. I had not given sufficient thought to it.

That it why it is best to use military time.
0001 UT and 0002 UT would be minutes after midnight Universal Time. At 0500 UT, it would be 4:00 PM PST.