While Tarpan can technically be performed daily after a morning bath, the most auspicious and significant period is Pitru Paksha, a 16-lunar-day period (usually in September-October) specifically dedicated to ancestral worship. Gaya hosts a large Pitru Paksha Mela during this time, attracting millions. Performing Tarpan on the specific ‘tithi’ (lunar day) corresponding to the ancestor’s death anniversary during Pitru Paksha is considered highly effective. Amavasya (new moon days) are also auspicious.