From my experience, it takes at least 48 hours but never more than a week. If a release doesn’t appear in the Roon dataset after a week, it either
-
didn’t make it into it because Roon might not deem it to be different enough from what it already has, see
Release versions missing in Roon (present in Musicbrainz)
or -
it didn’t make it as a version of an existing release but as a new release, which on rare occasions also may not be found easily or only with a certain search term.