Mahashtami – the third day
Mahashtami is the D day of Durgapuja, Mother Goddess have slain the buffalo demon on Mahashtami Sandhikshan in Spring Durgapuja or Basantipuja, and Ramchandra killed Ravana on Mahashtami Sandhikshan, Sandhikshan is when Ashtami and Navami meet. No Hindu tithis don’t follow clocks or common calendars. Every home that holds puja in orthodox way offers own special puja to the Goddess on this day.
Wish you all a very blessed Durgapuja!