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: Sunday 29th September 2019
Pratipada
Ghatasthapana
Chandra Darshan
Shailputri Puja
Navratri color of the day – Orange
Navratri Day 2: Monday 30th September 2019
Dwitiya
Brahmacharini Puja
Navratri color of the day – White
Navratri Day 3: Tuesday 1st October 2019
Tritiya
Sindoor Tritiya
Chandraghanta Puja
Navratri color of the day – Red
Navratri Day 4: Wednesday 2nd October 2019
Chaturthi
Kushmanda Puja
Varad Vinayaka Chauth
Upang Lalita Vrat
Navratri color of the day – Royal Blue
Navratri Day 5: Thursday 3rd October 2019
Panchami
Skandamata Puja
Navratri color of the day – Yellow
Navratri Day 6: Friday 4th October 2019
Shashthi
Saraswati Awahan
Katyayani Puja
Navratri color of the day – Green
Navratri Day 7: Saturday 5th October 2019
Saptami
Saraswati Puja
Kalaratri Puja
Navratri color of the day – Grey
Navratri Day 8: Sunday 6th October 2019
Ashtami
Durga Ashtami
Mahagauri Puja
Sandhi Puja, Maha Navami
Navratri color of the day – Purple
Navratri Day 9: Monday 7th October 2019
Navami
Ayudha Puja, Navami Homa
Navratri Parana
Navratri color of the day – Peacock Green
Navratri Day 10: Tuesday 8th October 2019
Dashami
Durga Visarjan, Vijayadashami