For Ayambil (including drinking boiled water / pāyo), the simple traditional rule is:

1. Start time (when to begin pāyo / water)

- Start after Navkarsi, i.e. about 48 minutes after sunrise. - Before Navkarsi, you should not drink water (even boiled) according to traditional maryādā.

1. Meal time (Ayambil bhojan)

- Take your one plain meal in the day, normally at porsi time – roughly 3 hours after sunrise, and always finish well before sunset.

1. Stop time (till when pāyo is allowed)

- Boiled water (uṣṇapāni) is generally allowed only in daylight, from Navkarsi till sunset. - After sunset (or whatever exact cut‑off your sangh follows), no water or food.

1. Important note

- Exact timings (e.g. whether to stop water exactly at sunset or some minutes before) can vary by sangh / guru’s pachkhan. - Always follow the maryādā given by your own Acharya / guru / local sangh first.

For a simple step‑by‑step guide to doing Ayambil you can read more here