Timeout for AFNetworking

I am using AFJSONRequestOperation to upload images.

When loading image numbers, some requests are not executed with a timeout error.

I tried

AFJSONRequestOperation *operation = ...
[operation start];

and

AFJSONRequestOperation *operation = ...
[operations addObject:operation];
...
[client enqueueBatchOfHTTPRequestOperations:operations progressBlock:nil completionBlock:nil];

However, still no luck.

I think the countdown begins when the operation is created.

So, should I plan queries one by one for my own algorithm?