I recently started participating in CodeForces contest and am a complete beginner. I currently have a basic knowledge of C++. I can write C++ code for basic problems and programs. Please tell me the rating that I should aim for and how much time it could take on average to reach that rating on CodeForces for clearing ZCO and INOI and getting into the IOITC.

Please answer according to the Indian Informatics Olympiad competition and participation only.