The (deceased) grandfather become gratified with the Shraddha that may be performed on any day. I shall, however, tell you now what the merits and demerits are of the respective lunar days.
सर्वेष्वहःसु प्रीयन्ते कृते श्राद्धे पितामहाः। प्रवक्ष्यामि तु ते सर्वास्तिथ्यातिथ्यगुणागुणान्॥