In Jain practice, there isn’t a fixed number of days after Athai Parṇa when you may eat oats. The emphasis is on easing back to food gradually, with meals that are simple, warm, and lightly cooked. Start with water, then a very light parna meal, and slowly reintroduce solid foods over the next day or two, depending on how you feel and under the guidance of your guru or sangh. Oats can be considered acceptable only if they are plain, well-cooked, and eaten in small, mindful quantities as part of a light, sattvik meal after you have begun your Parṇa recovery. If in doubt, follow your local practice.

• Parṇa guidance (general): start with boiled water, then light, simple foods and gradually return to normal diet. You break the fast within the prescribed Parṇa time. ( jainknowledge.com)
• Athai and Parṇa basics (context and gradual reintroduction after Athai): Athai involves eight meals and Parṇa is the careful closing and reintroduction of food. Follow the gradual progression described for Parṇa. ( jainknowledge.com)

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