Hours which are past midnight are suffixed with next day date. In Panchang day starts and ends with sunrise.
In South India, Saraswati Puja is done on the last day of Navratri and it is observed on the same day as Ayudha Puja. On the next day of Saraswati Puja children between the age of 4 and 5 go through Vidyarambham ceremony.
However in the Northern and the Western India, Goddess Saraswati is worshipped for four days during Navratri. The Puja starts with Saraswati Avahan which is followed by Saraswati Puja, Saraswati Balidan and Saraswati Visarjan.