Krishna Dwitiya is the seventeenth tithi overall, the second lunar day of the waning fortnight. It carries the character of the second tithi, a Bhadra or wholesome day with Brahma as its traditional deity, but set now in the diminishing light of the dark half. The waning gibbous Moon rises later each night and is past full. The panchanga distinguishes the two fortnights in judging auspicious times, and while the bright fortnight is generally preferred for new undertakings, the dark fortnight has its own suitable observances, including rites for the ancestors. These are the conventions of the Hindu luni-solar calendar, in which every tithi is counted twice a month, once in each paksha, and read partly through its number and partly through the fortnight it falls in.
Because Brahma is assigned as presiding deity to the second tithi in both fortnights, the waning Dwitiya inherits the same creator association as its waxing counterpart even while occupying the structurally opposite, diminishing half of the month, which is a clear instance of how the panchanga's deity assignments track the tithi's fixed number rather than its waxing or waning status. Shraddha rites for ancestors, while concentrated most heavily around Amavasya and the Pitru Paksha fortnight, can in principle be performed on the specific tithi corresponding to a deceased relative's date of death each month, so a family's personal ritual calendar of ancestral observance runs in parallel to, and independently of, the fixed public festival calendar built around particular numbered tithis.