I have a little information on Ashtami Puja, I don't have the information on step by step process or chandi path, but normal puja requirements and how the Sandhi Puja is performed on Ashtami, see if that helps.
Ashtami:
This is the day of Goddess Durga. She is offered a new saree and a bhog (offering) of kheer-puri.
Items needed for Ashtami Puja of Goddess Durga:
One sari for Durga and new clothes for Lakshmi, Saraswati, Chandi, Kartik, Ganesh, Shiva, Vishnu, nine planets, the peacock, mouse, lion, demon, buffalo, ox, snake, Jaya, Bijoya and Ram.
Other items required is one dantakashto, 40 or 22 finger rings made of ‘kusha’ (The kusha leaves are an emblem of purity and divinity. The kusha leaves are a type of grass used as sacramental rings worn while performing sacraments). Other items required in the pooja are: one nose ring, iron, two conch shells, a box of vermillion, flowers, a garland, belpatra (pan) garland, fruits for bhog (offering).
Items for aarti - 40 or 22 bowls of ‘madhupakka’ (a mixture of honey, curd, ghee and sugar for oblation), honey, sugar, curd, ghee , 40 or 22 noibiddos - Food Offering (we basically say it in gujarati as Nived), four small noibiddos , one chandmala , one dhoti
For Sandhi Puja -
Flowers, gold ring, a bronze bowl for madhupakka , a small sari, main noibiddo , one small noibiddo , one plate, one pitcher, iron, 108 lotus flowers, one nose ring, one pillow, a mat, a chandmala , 108 earthen lamps, items for bhog , and items for the arati .
What Is Sandhi Puja?
Sandhi Puja is an important ritual performed during Durga Puja. It is performed at the juncture of Ashtami and Navami.
It is believed that Goddess Chamunda emerged at this moment to kill Chando and Mundo, the two generals of the demon king Mahishasur.
Legend:
When Goddess Durga was engaged in a fierce fight with Mahishasur, Chando and Mundo attacked her from the rear. The goddess was clad in a yellow sari and emitting a golden glow. She carried the crescent of the moon on her head and wielded different weapons in her ten arms. When she saw Chando and Mundo, she opened her third eye from which emerged the fierce Goddess Chamunda. She had a fearsome countenance with a bloody tongue and red eyes. She leapt forward with a piercing shriek and killed the two demons. This happened at the juncture of the eighth and the ninth lunar days and hence, Sandhi Puja for Goddess Chamunda is performed at this time.
Sandhikhan:
The puja begins 24 minutes before the end of Ashtami and ends after 24 minutes of Navami. This period is called Sandhikhan.
In olden days, a bronze bowl with a tiny hole was placed in water. The bowl was designed such that it took exactly 24 minutes for it to submerge in water. The moment it submerged, canon balls were fired to announce the Sandhikhan.
The puja: Sandhi Puja requires 108 lotus flowers, a single fruit, dry rice grain for "noibiddo", 108 earthen lamps, clothes, jewellery, hibiscus garlands and wood apple (bel) leaves.
The almost non existent rituals which underwent changes with the changes in the society can still be seen in some of the 200-250 year old Pujas.
