Final answer:
On an Air Only Reservation with Trip Flex, changes are allowed until 24 hours prior to the flight departure.
Step-by-step explanation:
On an Air Only Reservation with Trip Flex, changes are allowed up until 24 hours prior to their flight departure. Trip Flex is a fee-based service offered by certain airlines that allows passengers to make changes to their flight reservations without incurring hefty change fees. With Trip Flex, passengers can change their flight dates, times, or even destinations up to 24 hours before the scheduled departure time.