Hours which are past midnight are suffixed with next day date. In Panchang day starts and ends with sunrise.
Navami Shraddha is done for those deceased family members who died on Navami Tithi, including both Shukla and Krishna Paksha Navami.
Navami Shraddha Tithi is also known as Matra Navami (मातृनवमी). This Tithi is the most suitable day to perform mother's Shraddha. It is believed that doing Shraddha on this Tithi appeases all deceased female members in the family.
Navami Shraddha is also known as Naumi Shraddha and Avidhava Shraddha.
Pitru Paksha Shraddhas are Parvan Shraddhas (पार्वण श्राद्ध) and auspicious time to perform them 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.