https://www.united.com/web/en-us/content/reservations/refunds/24-hour-booking-policy.aspx

를 보시면 다음과 같은 룰이 있네요.

24-Hour Flexible Booking Policy

United's 24-hour flexible booking policy allows the flexibility to make changes to select reservations within 24 hours of purchasing your ticket, without incurring change fees if you made your purchase one week or more prior to the original scheduled departure flight. This includes canceling your reservation and requesting a 100% refund of the ticket price. Although Basic Economy reservations are not eligible for changes within 24 hours, they are still eligible for a full refund if you cancel within 24 hours and you made your purchase one week or more prior to the original scheduled departure flight. Please view the terms and conditions below.

Terms and conditions

• Applies to tickets booked at united.com or with the United Customer Contact Center.
• The 24-hour timeframe begins at the time your ticket is purchased.
• Requests for refunds will be credited back in the original form of payment, with the exception of purchases made with a United Gift Certificate, which will be credited back in the form of electronic travel certificates.
• Group tickets and tickets purchased using Western Union, cash or e-certificates are excluded.
• Reservations that are being held but have not yet been purchased are excluded.
• Any FareLock^SM fees paid to hold a reservation will not be refunded.