If the user has the 'delete own posts' permission, the delete time limit applies after the edit time limit.
The primary purpose of this addon was to allow a day or two for users to delete their own posts and then prevent deleting of older posts as that was causing performance issues in super-long very old threads. It would cause XF1.x style perma-post links to repeatedly shift which was a user UX issue.
It isn't too much of an issue now that XF2.x changed the link style; but it still causes post-on-page links to shift and the underlying performance issues are still there if a user decides to delete posts one-by-one in a +10k reply thread.
