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