The Hindu calendar's lunar day is not a day. It is 12° of the Moon pulling away from the Sun, so it runs anywhere from 19 to 26 hours.

Thirty tithis make a lunar month, and the eighth and twenty-third land on the quarter moons. Because the Moon's speed varies through its orbit, a tithi stretches and shrinks, and one can occasionally be skipped entirely. It is the same angle this page calls elongation, counted in a system several thousand years older than the word.