ソート済みのNSArrayに、順番を保ちつつ新しいデータを追加する ref: http://qiita.com/roothybrid7/items/15fd39af876a9b7caa90

file0.txt

NSArray *sourceData = @[
                        @{@"id": @"A", @"createdAt": @1234533333},
                        @{@"id": @"B", @"createdAt": @1234599999},
                        @{@"id": @"C", @"createdAt": @1234511111},
                        @{@"id": @"D", @"createdAt": @1234522222},
                        @{@"id": @"E", @"createdAt": @1234599999},
                        ];

// Sort descritors
NSSortDescriptor *createdAtSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"createdAt" ascending:NO];
NSSortDescriptor *idSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"id" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)];

// 並び替え(作成日降順、ID昇順)
NSMutableArray *objects = [sourceData sortedArrayUsingDescriptors:@[createdAtSortDescriptor, idSortDescriptor]].mutableCopy;
/*! ->
    @[
        @{@"id": @"B", @"createdAt": @1234599999},
        @{@"id": @"E", @"createdAt": @1234599999},
        @{@"id": @"A", @"createdAt": @1234533333},
        @{@"id": @"D", @"createdAt": @1234522222},
        @{@"id": @"C", @"createdAt": @1234511111},
    ];
 */

// 新規データ
NSDictionary *newObject = @{@"id": @"F", @"createdAt": @1234544444};

// NSBinarySearchingFirstEqualも合わせて指定すると最初にマッチしたIndexを返す
NSUInteger searchOptions = NSBinarySearchingInsertionIndex | NSBinarySearchingFirstEqual;
// 追加するデータのIndexの取得
NSInteger newIndex = [objects indexOfObject:newObject inSortedRange:NSMakeRange(0, objects.count) options:searchOptions usingComparator:^NSComparisonResult(NSDictionary *d1, NSDictionary *d2) {
    if (![d1[@"createdAt"] isEqualToNumber:d2[@"createdAt"]]) {
        return [d2[@"createdAt"] compare:d1[@"createdAt"]];
    }
    return [d1[@"id"] localizedCaseInsensitiveCompare:d2[@"id"]];
}];
// -> 2

[objects insertObject:newObject atIndex:newIndex];

/*! ->
    @[
        @{@"id": @"B", @"createdAt": @1234599999},
        @{@"id": @"E", @"createdAt": @1234599999},
        @{@"id": @"F", @"createdAt": @1234544444},
        @{@"id": @"A", @"createdAt": @1234533333},
        @{@"id": @"D", @"createdAt": @1234522222},
        @{@"id": @"C", @"createdAt": @1234511111},
    ];
 */