Hours which are past midnight are suffixed with next day date. In Panchang day starts and ends with sunrise.
Purnima Shraddha is also known as Shraddhi Purnima and Proshthapadi Purnima Shraddha (प्रोष्ठपदी पूर्णिमा).
It should be noted that Mahalaya Shraddha for those who died on Purnima Tithi is done on Amavasya Shraddha Tithi and not on Bhadrapada Purnima. Although Bhadrapada Purnima Shraddha falls one day before Pitru Paksha, it is not part of Pitru Paksha. Usually, Pitru Paksha starts on the next day of Bhadrapada Purnima Shraddha.
Bhadrapada Purnima Shraddha, like Pitru Paksha Shraddha, is Parvan Shraddha (पार्वण श्राद्ध) and auspicious time to perform it is either Kutup Muhurat and Rohina etc. Muhurat after that till Aparahna Kala gets over. Tarpan (तर्पण) is done at the end of the Shraddha.