NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setLocale:[NSLocale currentLocale]];
[formatter setDateStyle:NSDateFormatterNoStyle];
[formatter setTimeStyle:NSDateFormatterShortStyle];
NSString *dateString = [formatter stringFromDate:[NSDate date]];
NSRange amRange = [dateString rangeOfString:[formatter AMSymbol]];
NSRange pmRange = [dateString rangeOfString:[formatter PMSymbol]];
BOOL is24h = (amRange.location == NSNotFound && pmRange.location == NSNotFound);
[formatter release];
NSLog(@"%@n",(is24h ? @"YES" : @"NO"));

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"hh:mm a"]; //I suggest using lower case h for hour
NSLog(@"Formatted Date: %@", [formatter stringFromDate:[NSDate date]]);
[formatter release];