title: AFNetworking timeout is not working
body: <p>I am using AFNetworking V2.5.4. </p>
  
  <p>The default timeout for AFN is 60s, this is too long for my app. I want to set it as 20s. 
  So I tried follow code <code>manager.requestSerializer.timeoutInterval = 20;</code>
  But it's not working.  I searched some post saying I need add <code>[manager.requestSerializer willChangeValueForKey:@"timeoutInterval"];
      manager.requestSerializer.timeoutInterval = 3;
      [manager.requestSerializer didChangeValueForKey:@"timeoutInterval"];</code></p>
  
  <p>Still, it's not working.</p>
  
  <p>Follow is my code piece </p>
  
  <pre><code>+ (AFHTTPRequestOperation *)sendRequestWithRequest:(NSMutableURLRequest*) request
                                         manager:(AFHTTPRequestOperationManager *)manager
                                         success:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                                         failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure{
  [manager.requestSerializer willChangeValueForKey:@"timeoutInterval"];
  manager.requestSerializer.timeoutInterval = 3;
  [manager.requestSerializer didChangeValueForKey:@"timeoutInterval"];
  NSLog(@"manager %@, start time %lf",manager, [[NSDate date] timeIntervalSince1970]);
  AFHTTPRequestOperation *operation = [manager HTTPRequestOperationWithRequest:request
                                                                       success:^(AFHTTPRequestOperation *operation,  id responseObject) {
                                                                           if (operation.response.statusCode) {
                                                                               success(operation, responseObject);
                                                                           }else{
                                                                               failure(operation, nil);
                                                                           }
                                                                       }
                                                                       failure:^(AFHTTPRequestOperation *operation,  NSError *error) {
                                                                              failure(operation, error);
                                                                       }];
  
  [manager.operationQueue addOperation:operation];
  return operation;}
  </code></pre>