For monthly Sangkramanam-s, punya kala periods are specified – Vishu for 20 nazhigai-s, Vishnupati 16 nazhigai-s and Shadasheeti 60 nazhigai-s; one can infer from the nazhigai-s of vishu and vishnupati that if the sangkramanam occurs during the first part of the night, that tarpanam is performed the previous day and if occurs during later part of the night, tarpanam is performed the following day. With regards to Shadaseeti, how should we read the 60 nazhigai-s after the birth of the new month? Daytime is only 30 nazhigai-s. And there are separate regulations related to nighttime occurrences. Kindly clarify.

If the Sangkramanam is during the first half of the night, punya kalam, and tarpanam are on the previous days. If it is during the later parts of the night, tarpanam, etc. are done during the following day. If it occurs middle of the night, according to a statement, tarpanam can be done on both days. Even when Sangkramanam is in the middle of the night, if it is Shadasheeti punya kalam, tarpanam must be done only on the next day. The only exception to this rule is during the two Ayana kalams – regardless of whether it is Dakshinayanan or Uttarayanam, tarpanam must be performed only in the Uttarayanam.
During other months, even if it is Sadasheeti punya kalam and even when Sangramanam is during the first part of the night, tarpanam is performed only during midday (According to the statement ‘madhyAnAn upari kriya’).