I thought I saw something answering this on SO recently but now I can't find it. Here is the code I am using now to determine if settings are for 24 hour time display. It works for me in the US, but I don't know if it will work in all locales. Is this sufficient or is there a better way to find out the current setting for this?
+(BOOL) use24HourClock
{
BOOL using24HourClock = NO;
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setLocale: [NSLocale currentLocale]];
[dateFormatter setDateStyle:kCFDateFormatterNoStyle];
[dateFormatter setTimeStyle:kCFDateFormatterShortStyle];
// get date/time (1Jan2001 0000UTC)
NSDate* midnight = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:0];
NSString* dateString = [dateFormatter stringFromDate: midnight];
// dateString will either be "15:00" or "16:00" (depending on DST) or
// it will be "4:00 PM" or "3:00 PM" (depending on DST)
using24HourClock = ([dateString length] == 5);
[midnight release];
[dateFormatter release];
return using24HourClock;
}