It sounds like you’re asking about “pachkhan (pachchakkhān)” related to eating before sunrise.

Core Jain rule (both Śvetāmbara and Digambara):

• One should not eat before sunrise or after sunset. The standard lay vow is Navkārśī (first food only after sunrise, traditionally after 48 minutes). Eating before sunrise is not permitted.

When is a pachkhan used here?

• Only if there is a genuine health need (medicine). Then one may take an Aushadhi Pachchakkhān (a limited, specific vow) to take only that medicine before sunrise. It must be precise about item, quantity, time, and duration, and taken from a Guru; if none is available, take it in front of a Jina idol or sacred text with due reverence. Outside that exact allowance, no food/drink is taken before sunrise.

Simple Aushadhi Pachchakkhān (sample wording)

• “With devotion to Arihanta, Siddha, Āchārya, Upādhyāya, and Sādhu, I, [name], at [place], on [date], take this limited Aushadhi Pachchakkhān: Due to [health reason], I will take only [name of medicine/liquid], quantity [x], at [time] before sunrise, for [number] day(s). This is only as medicine, not for taste. Apart from this, I will not take any food or drink before sunrise. Micchāmi Dukkaḍaṁ.”

Notes by tradition

• Śvetāmbara: The practice of precise pachkhan formulas (including Porsi/Sadporsi/Upvās) is emphasized; exceptions for medicine are allowed with a clear, time-bound vow.
• Digambara: The rule of day-eating (no night/ pre-sunrise eating) is equally strict; “aushadhi-grahan” with pratyākhyāna (limited vow) is allowed for health, with specific limits as above.

Related basics

• If your intent was to ask “When to take pachkhan for upvās?” — take it before sunrise on that day, ideally after morning pratikraman, and then observe the fast as vowed.
• For structured meal-time vows like Porsi/Sadporsi (first meal 3 or 4.5 hours after sunrise), see:
• For “Upvās nu Pachkhan,” an example and explanation:

Essence

• Do not eat before sunrise.
• Use a pachkhan only to allow necessary medicine before sunrise, with strict limits, spiritual intent, and repentance (Micchāmi Dukkaḍaṁ) if any lapse occurs.