In Jainism there isn’t a single universal rule about the exact time to drink water on Upwas (fasting) days. Practices vary by tradition and local custom.

• Digambar and Shwetambar communities often have their own detailed rules for a given vrat, so the allowed times for drinking water can differ between them.
• In many Upwas observances, people focus on abstaining from food and following the vrata rules for the day, and water is often permitted as needed. Some households/regions may specify drinking water after sunrise or after completing certain ritual periods, while others may allow water throughout the day and night.

If you want the precise guideline for your tradition or a specific Upwas, please check with your local Jyoti/jain guru or refer to the rules your family follows, as they’ll give you the exact timing for your context.