You should set timeout interval in session configuration
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
configuration.timeoutIntervalForRequest = 20;
configuration.timeoutIntervalForResource = 20;
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
// in case if you are using AFNetworking
// AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc] initWithSessionConfiguration:configuration];