• Solah Upvās (Solbhatt / Solapakhī) is sixteen days of fasting. The core rule is no solid food for the entire period. In many Jain communities, this is practiced with light rules about liquids taken only during daylight. ( jainknowledge.com)

• Regarding eating at night: a common practice during fasts is Ratri Bhojan Tyag — not eating after sunset. Some sanghs follow this strictly, while others allow limited liquids (like boiled water) during the daytime window and avoid solid food after sunset. The exact allowance can vary by Digambar/Shwetambar tradition and by local sangh guidance. ( journals.lww.com)

• In short: during Solbhatt you do not eat solid food for sixteen days; many follow “no food after sunset” (Ratri Bhojan Tyag), and liquids are usually limited to a daylight window, with exact rules varying by community. ( jainknowledge.com)

You can read more about these fasts and their common rules here and here .