Introduction:
The ideal duration for an Economics Optional study plan varies depending on various factors such as the candidate's prior knowledge, time availability, and dedication towards the subject. However, a well-structured study plan for Economics Optional should cover all the essential topics, provide ample time for revision, and allow for practice through solving previous years' question papers and mock tests. Here is a suggested study plan that can be followed for a duration of 3-4 months.

Study Plan:

1. Understanding the Syllabus:
- Go through the UPSC syllabus for Economics Optional.
- Identify the topics that need more focus and those that can be covered quickly.

2. Collecting Study Material:
- Gather all the required study materials such as textbooks, reference books, and notes.
- Ensure that the study material is comprehensive and covers the entire syllabus.

3. Creating a Study Schedule:
- Divide the entire syllabus into smaller topics and allocate specific time slots for each topic.
- Ensure that the schedule is realistic and flexible to accommodate unforeseen events.

4. Conceptual Understanding:
- Start with the basic concepts of microeconomics and macroeconomics.
- Understand the theories, models, and principles of economics.
- Focus on topics like demand and supply, production and cost, market structures, national income accounting, inflation, fiscal and monetary policies, etc.

5. Application and Analysis:
- Apply the economic theories and models to real-world scenarios.
- Analyze various economic problems and policy implications.
- Understand the interlinkages between different economic concepts.

6. Case Studies and Examples:
- Study case studies and examples to enhance your understanding.
- Analyze the economic implications of real-life situations.
- Refer to newspapers, magazines, and economic journals for relevant case studies.

7. Revision:
- Regularly revise the topics covered to reinforce your understanding.
- Make concise notes for quick revision.
- Solve previous years' question papers and mock tests to assess your preparation.

8. Time Management:
- Allocate more time to difficult topics and areas of weakness.
- Focus on improving speed and accuracy while solving numerical problems.
- Practice time-bound mock tests to enhance your time management skills.

9. Stay Updated:
- Keep yourself updated with current economic affairs and government policies.
- Follow reputable newspapers, magazines, and online sources for the latest economic news.

10. Seek Guidance:
- If needed, seek guidance from experienced teachers or mentors.
- Join online forums or discussion groups to clarify doubts and get insights from fellow aspirants.

Conclusion:
The ideal duration for an Economics Optional study plan is subjective and depends on individual circumstances. However, with a well-structured study plan covering the entire syllabus, regular revision, and practice, candidates can achieve a good command over the subject within a duration of 3-4 months. It is essential to stay dedicated, disciplined, and consistent throughout the preparation journey to excel in the Economics Optional paper of the UPSC exam.