You can cancel your ticket within the last 24 hours of your booking. There is no option to cancel the flight on the scheduled day. However, Delta Airlines have some specific policies in case of cancellation, and you can apply for a refund. In case of booking of flights within the last 24 hours, you can also find details about the 24-hour Risk-Free Cancellation. A cancellation fee is applicable for canceling non-refundable tickets.