tithinirṇaya

(‘choosing the day [according to the lunar calendar]’)

Treatises dealing with the imparting of mantras, like the Mantrayogasaṁhitā, have specified which days of the lunar calendar (called tithis) are suitable for it and which are not.

The following days are auspicious: dvitīya (second day); tṛtīyā (third day); pañcamī (fifth day); saptamī (seventh day); daśamī (tenth day); ekādaśī (eleventh day); dvādaśī (twelfth day); pūrṇimā (full-moon day).

The other days, including amāvāsyā (new-moon day), are considered inauspicious.