Hours which are past midnight are suffixed with next day date. In Panchang day starts and ends with sunrise.
Dwadashi Shraddha is done for those deceased family members who died on Dwadashi Tithi, including both Shukla and Krishna Paksha Dwadashi.
Dwadashi Shraddha Tithi is also suitable to perform Shraddha for those who had taken renunciation (संन्यास) before death.
Dwadashi Shraddha is also known as Baras 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.