AFHTTPRequestOperationManagerにはタイムアウトとキャッシュポリシーを設定するプロパティが無いので
カテゴリクラスを作っておくと便利です。

AFHTTPRequestOperationManagerのカテゴリメソッド

- (AFHTTPRequestOperation *)GET:(NSString *)URLString
                     parameters:(NSDictionary *)parameters
                timeoutInterval:(NSTimeInterval)timeoutInterval
					  cachePolicy:(NSURLRequestCachePolicy)cachePolicy
                        success:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                        failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
{
    NSError* error = nil;
    
    NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:@"GET"
                                                                   URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString]
                                                                  parameters:parameters
                                                                       error:&error];
    
    
    [request setTimeoutInterval:timeoutInterval];
    [request setCachePolicy:cachePolicy];
    AFHTTPRequestOperation *operation = [self HTTPRequestOperationWithRequest:request success:success failure:failure];
    [self.operationQueue addOperation:operation];
    
    return operation;
}