Chhath Puja ritual starts on the fourth day of Kartika month, Puja begins with Nahay Khay.The word Nahay Khay, Nahai means to bathe, and Khai means to eat. On the first day of Nahai Khai, devotees take a holy bath in a holy lake or river, to purify their sins. Then, they worship Lord Surya. Water from the holy river is carried to homes, which is later used in cooking food offerings for Surya which then continues for the next 36 hours.
On this day devotees eats rice, gram pulses, and pumpkin vegetables sans onion and garlic. After eating the food sometime mid-noon, the Parvatin (devotee) starts the waterless-fast which is broken only the next day evening while observing 'Kharna' the second day of Chhath Puja. During this period of three nights and four days, the worshiper observes purity and sleeps on the floor. Since it falls in winter, a bed on rice straws is made by putting a blanket on it.
Basically on this day the devotees buy all the essenital items like necessary for Chhath Puja.
Chhath Puja 'Nahay Khay': Muhurat
Sunrise at 06:35
Sunset at 17:34.