Google‘s Gary Illyes recommends leaving the redirects in place for at least a year. It aids in the proper transmission of ranking signals. Google has previously advised that the redirects be left in place for a year or perhaps longer. It’s one of the best practices in general, not something that has a direct impact on the ranking signals.
After one year, site owners can delete a redirect. Google will continue to forward signals indefinitely. This is Google‘s first response on the question of how long redirects should be kept on a website.
Gary advised that the redirects be kept in place for as long as feasible. The minimal time frame for it is one year. This time limit gives Google enough time to move all of its signals to the new URLs. At the same time, it aids in the recrawling and reassignment of links on other websites that lead to your old URLs.
From the user’s standpoint, it’s preferable to preserve the redirects indefinitely. For the most part, redirection are slow for the users. As a result, it is preferable to update the links, as well as any additional high-volume links from other websites that can lead to the new URLs.
Illyes also responded to a number of queries about the tweet. When a signal is passed from one URL to the next, it will remain in that state indefinitely.
Google takes around a year to forward all of the signals. This is why Gary recommends keeping the redirect alive for at least that long.
As a result, if at all possible, keep the redirects active for as long as possible. It will improve the overall user experience.