Allegiant Air provides customers with the ability to hold payments for booked tickets 24 hours a day. Ticket prices and booking locations are held for 24 hours and payments can be made after the end of the period, but changes made during this time frame may affect the price of the ticket. Allegiant Air cancellation policy says the cancellation fee within 24 hours is the same as the holding fee.

For all non-refundable tickets, all charges for optional services that cannot be achieved due to overbooking or flight cancellations will be refunded in accordance with the product terms and conditions. The ticket is not valid and refunds for the ticket purchased will be given in accordance with fair rules. If the ticket is non-refundable, it can be used to pay for a new ticket and must be booked in the same name as the passenger. Partially used tickets may or may not be refunded according to the ticket's fare rules. Some tickets may or may not be refunded in accordance with the fare rules that apply to tickets purchased.
https://www.cancellation-policy.com/allegiant-airlines-cancellation-policy