Information about duplicate pages

[Bob253builder09]

In the excluded section of the Search Console, there are 36 pages titled "Duplicate without user-selected canonical" present. These pages were generated unknowingly due to an automatic feature of the CMS I use, creating feed pages. I have intervened by setting them all to return a 404 error. However, these pages have not been removed from the coverage report for about a month. How long does it take for Google to remove these pages from duplicates? The Googlebot does not access these pages at all. Is there any additional action I need to take?