Most of the religious books Dharma Sindhu, Nirnaya Sindhu and Vratraj suggest Lakshmi Puja on Diwali during Pradosh time after sunset while Amavasya Tithi prevails. If Amavasya Tithi is getting over before sunset then Lakshmi Puja is done on Chaturdashi Tithi when Amavasya prevails after sunset. As most of these religious books don't mention Muhurat for Puja timings based on Vedic astrology, many astrologers provide various auspicious Puja timings for Lakshmi Puja on Diwali. Although there are various opinions on the best Muhurat for Lakshmi-Ganesha Puja on Diwali, the most astrologers agree that Lakshmi Puja should be done during fixed Lagna. The Lagna is most significant factor while considering the Muhurat for most activities. In Vedic astrology there are twelve Lagna in twenty-four hours and those are categorized as fixed, movable and common. The following four Lagna(s) are considered fixed in nature and are considered good for Lakshmi Puja.
As Goddess Lakshmi is movable and never stays at a single place for long, there are always attempts to make Her fixed or prolong Her stay at one place by worshipping Her during a fixed Lagna. It is believed that worshipping Goddess Lakshmi during fixed Lagna would make Her stable or at least prolong Her stay at one place.
As per legends, Goddess Lakshmi came out of the milky ocean on the day of Dhantrayodashi and chose Lord Vishnu as Her husband on the day of Diwali. Hence Diwali Amavasya is considered the most appropriate day to appease the Goddess of wealth and prosperity. On the day of Amavasya during Diwali festivities, Vrishchika Lagna prevails in morning, Kumbha Lagna during afternoon, Vrishabha Lagna during evening and Simha Lagna during midnight. Hence Vrishabha Lagna is considered the most significant as it overlaps with Pradosh just after sunset. However due to some unavoidable circumstances, one is not able to perform Lakshmi Puja during Pradosh one can chose fixed Lagna Muhurat available during Amavasya.