Can shaving be done after punya kalam during the eclipse by both those who perform tharpanam and those who do not perform tharpanam? Should we partake tiffin at night after performing tharpanam? For example, the recent moon eclipse.

Tiffin is not a must for grahana tharpanam. Haircuts or shaving is not done normally during a punya kalam; as it is a tharpana day immediately after the eclipse, it is not allowed. It can be done on the day that follows the day after the day of the eclipse. If the day is prathamai then it is not in practice to shave. There is no mention of shaving specifically in scriptures which implies it is not allowed.