It took a bit to find it, but this is on the SW website:
“7
Flight credit expiration: To receive a flight credit, you must cancel your flight at least 10 minutes prior to the flight’s original scheduled departure time. If you do not cancel, your points and funds may be forfeited.
Learn more. Business Select® (Choice Extra), Anytime (Choice Preferred), and Wanna Get Away Plus® (Choice) Transferable Flight
Credits created from reservations booked and ticketed and/or changed on or after May 28, 2025 expire twelve months from the date the fare was purchased and ticketed. Basic fare flight credits expire six months from the date the fare was purchased and ticketed.”