The source – developers.google.com
Google search engineer Harry Ilsh tweeted about saving redirects.
According to SEO, it is advisable to leave them for at least a year. This will help ensure that all signals are constantly being transmitted to the new URL. But even if after a year it is decided to delete the redirect, it is advisable for users to keep them forever. And it's not about a year since inception, but since their first Google crawl.
hands up if you asked us recently for how long you should keep redirects in place!— Gary 鯨理／경리 Illyes (@methode) July 21, 2021
i have a concrete answer now: at least 1 year.
(but try keeping them indefinitely if you can for your users).
As a rule, redirects increase the page load time. So the recommendation to update URLs in your links and from other sites remains valid.