The Amavasya Tithi of the Hindu calendar month Kartik this year begins at 3:44 pm on October 20 and ends on October 21, says Drik Panchang. Astrologers suggest celebrating Diwali on October 20 as the Pradosh period would fall between 5:51 pm and 8:19 pm. October 21 is not ideal for Lakshmi Puja as the Amavasya period exceeds three Prahar.