Introduction:
Taking mock tests is an essential part of the preparation journey for any competitive exam, including UPSC. Mock tests help in assessing one's knowledge, identifying strengths and weaknesses, and improving overall performance. However, it is crucial to start taking mock tests at the right time to make the most of these practice exams.

Understanding the syllabus and exam pattern:
Before starting with mock tests, it is important to thoroughly understand the syllabus and exam pattern of the UPSC exam. This will give a clear idea of the topics to be covered and the structure of the exam. It is advisable to spend sufficient time studying the entire syllabus before attempting mock tests.

Completing the basic preparation:
Mock tests should not be taken at the initial stages of preparation. It is necessary to complete the basic preparation, including studying the core subjects, understanding concepts, and solving practice questions. This will provide a strong foundation and ensure that mock tests are more beneficial in assessing the level of preparation.

Revising and practicing:
Before starting with mock tests, it is important to revise the topics and concepts covered in the syllabus. This will help in refreshing the knowledge and ensuring a better performance in the mock tests. It is also advisable to solve previous year question papers and practice questions to get acquainted with the exam pattern and improve time management skills.

Starting with mock tests:
Once the basic preparation is complete, and sufficient revision and practice have been done, one can start taking mock tests. The ideal time to start with mock tests is around 3-4 months before the actual exam date. This allows for ample time to take multiple mock tests, analyze the performance, and work on the areas that need improvement.

Benefits of taking mock tests:
- Mock tests help in understanding the exam format and time management skills.
- They provide an opportunity to practice solving questions under exam-like conditions.
- Mock tests help in identifying weak areas and focusing on them for improvement.
- They help in building confidence and reducing exam-related anxiety.
- Mock tests also provide a benchmark to evaluate one's performance and track progress.

Conclusion:
Starting mock tests at the right time in the preparation journey is crucial for UPSC aspirants. It is advisable to complete the basic preparation, revise, and practice before starting with mock tests. The ideal time to begin with mock tests is around 3-4 months before the exam date, allowing sufficient time for analysis, improvement, and further practice. Taking mock tests regularly and analyzing the performance will help in achieving better results in the UPSC exam.