One other thing:
I've done some tests and there is a different formatting function which observes the system level "use 24 hour format" setting (haven't tested with rebooting the phone, though).
However:
On a phone that is set to Russian language, it's applied too.
On this phone, I happen to have that setting "off" -- so it comes out as "2:12 pm".
But we don't use am/pm in Russia, so "2 pm" is just "whoa, what is that?"
[ Or actually, we do but only when speaking, not in writing, and there is no shorthand, we say "8 in the morning" or "2 in the day" or "9 in the evening" ]
So let's say I make the change and some number of Russian users start seeing am/pm in their replies. This is wrong.
Some of them will contact me (unhappy about the change), some won't, and decide that the app is "broken".
Do I make a special case for Russian, based on the locale == "ru"?
Ok, what if someone from Russia actually wants to use the 12 hour am/pm format, a personal preference?
Do I now need to add yet another setting ("override system level setting")?
Will the users who think that "the app is broken" be able to find it without my help?
Is Russia the only country where there is no 12 hour am/pm format?
If not, what are the others, where do I get the full list?
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To summarize, something that looks like a really trivial change, may turn out to be very complicated if you consider the consequences.
In this respect, the "bigger" features (like the recent message view changes) are often easier.
