Sandhi Puja is a very significant ritual during Navratri Puja. It is performed at the point when Ashtami Tithi ends and Navami Tithi begins. This is believed to be the moment when Devi Chamunda appeared to kill the demons Chanda and Munda.
Sandhi Puja is dominant for two Ghatis or approximately lasts for 48 minutes. It is possible that Sandhi Puja Muhurta occurs at any time of the day and Sandhi Puja should be done during that time only.
You might also refer the complete Shardiya Navratri Calendar and Durga Puja Calendar.
Navratri Day 1: Wednesday 10th October 2018
Pratipada
Ghatasthapana
Chandra Darshan
Shailputri Puja
Brahmacharini Puja
Navratri color of the day – Royal Blue
Navratri Day 2: 11th October 2018
Tritiya
Sindoor Tritiya
Chandraghanta Puja
Navratri color of the day – Yellow
Navratri Day 3: Thursday 12th October 2018
Chaturthi
Kushmanda Puja
Varad Vinayaka Chauth
Navratri color of the day – Green
Navratri Day 4: Friday 13th October 2018
Panchami
Upang Lalita Vrat
Skandamata Puja
Navratri color of the day – Grey
Navratri Day 5: Saturday 14th October 2018
Panchami
Saraswati Awahan
Navratri color of the day – Orange
Navratri Day 6: Sunday 15th October 2018
Shashthi
Katyayani Puja
Navratri color of the day – White
Navratri Day 7: Monday 16th October 2018
Saptami
Saraswati Puja
Kalaratri Puja
Navratri color of the day – Red
Navratri Day 8: Tuesday 17th October 2018
Ashtami
Durga Ashtami
Mahagauri Puja
Sandhi Puja, Maha Navami
Navratri color of the day – Sky Blue
Navratri Day 9: Friday 18th October 2018
Navami
Ayudha Puja, Navami Homa
Navratri Parana
Navratri color of the day – Pink
Navratri Day 10: Saturday 19th October 2018
Dashami
Durga Visarjan, Vijayadashami
