Allegiant's 24-hour rule allows you to cancel your flight for a full refund within 24 hours of your initial booking, provided your scheduled departure date was at least one week (168 hours) away at the time of purchase. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) This is also known as the "24-hour reservation requirement" and is a consumer protection rule mandated by the Department of Transportation (DOT). Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) 

Key details of Allegiant's 24-hour rule

• Booking condition: This policy only applies if your flight was booked at least seven days before the scheduled departure date.
• Package bookings: The 24-hour rule does not apply if you booked your air transportation as part of a package that includes hotel or car rentals. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) 
• Method of cancellation: You can cancel online through the "Manage Travel" section on the Allegiant website or by contacting their reservation center.