Answer

The Jain practice you are describing is most likely Chauvihar.

In Chauvihar, a person does not eat or drink anything after sunset / before sleeping at night, and then eats or drinks only the next morning after waking up and doing proper prayer or mantra recitation, such as the Navkar Mantra.

Explanation

In Jain Dharma, night-eating is avoided because:

• At night, many tiny living beings may be present in food and water.
• Eating in darkness can unknowingly cause more himsa.
• It helps develop self-control and discipline.
• It supports spiritual alertness and purity.

There are related terms also:

• Chauvihar – no food and no water after the vow is taken, usually from evening/night until the next morning.
• Tivihar – no food, but boiled water may be allowed within proper time limits.
• Navkarshi – eating only after sunrise, after a proper gap and recitation of the Navkar Mantra.

Since you mentioned eating only after waking up in the morning and after reciting a mantra, it may also be connected with Navkarshi in the morning.

Takeaway

The night-time fasting practice is generally called Chauvihar, and the morning discipline of eating after sunrise and prayer is commonly called Navkarshi.