Amavasya and Purnima are the two most auspicious days of the month. This option is for a full year, a daan on both tithis, 24 in all.
The daan is made with a sankalp in your name, gotra and place. The temple's pandit ji takes the sankalp and makes the daan at the right muhurat.
Two temples in different places can keep the same Amavasya on different days, because sunrise comes at a different time. We take the day that holds at the temple you choose.
Each amount is charged 5 days before that daan's date, so the temple can buy the items in time.
After each daan, the temple sends a photo and the details of the sankalp.