In Jain dharma, there is no fixed rule like “you must perform Chaitri Poonam for X years.”

Chaitri Poonam is an annual tithi (full moon of Chaitra). Its main points:

• It is a very pavitra day connected with:

- Nirvan / Moksha of Pundarik Swami and many munis on Shatrunjay (Palitana) - Many great spiritual events remembered in Jain tradition.

• Jains usually observe it every year for their whole life:

- tirth-yatra to Shatrunjay (if possible) - fasting (upvas, ekasana, ayambil, etc.) - prabhavna, dan, and listening to pravachan

So:

• Even doing it once with full shraddha has great punya.
• Doing it every year, lifelong, is ideal.
• The “number of years” depends on your own vow (niyam) and guidance from your guru / pravachankar.

If you want to understand its importance in more detail, you can read here