Shashthi Shraddha could be performed for those souls who have departed on Shashthi Tithi. Deceased may be died in any Paksha or Lunar Fortnights i.e. Shukla Paksha (Bright Fortnight) or Krishna Paksha (Dark Fortnight).
Shashthi Shraddha is also known as Chhath Shraddha .
Read More : Cost of Pind Daan/ Asthi Visarjan/ Nagbali/ Narayan Bali/ Tripandi etc.
Pitri Paksha Shraddhas are Parvan Shraddhas (पार्वणश्राद्ध)
and auspicious time to perform them is Kutup Muhurt and Rohina Muhurt till Aparahna Kala (Post Meridian) gets over.
Tarpan (तर्पण) is done at the end of the Shraddha.