REQUIREMENTS FOR FILING A:
TAKEOFF ALTERNATE (TALT/) If wx at the ORIGIN AIRPORT are below the landing mins, you must specify an alternate airport within: 1 hour from the departure airport with one engine inoperative1)
ENROUTE ALTERNATE (RALT/)
LANDING ALTERNATE (ALTN/)
References: https://flighttrainingcentral.com/2025/02/how-to-choose-the-best-alternate-airport-for-your-ifr-flight-a-pilots-guide/ https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F/part-91/subpart-B/subject-group-ECFRef6e8c57f580cfd/section-91.169
1)
Aircraft with 3 or more engines may use an alternate that is not more than 2 hours at normal speed with 1 engine inoperative