None of the two settings seems to me to do what I suggested.
The courtesy setting doesn't hide that the post was edited, merely waits the courtesy time before time stamping the edit.
The maximum setting simply means that after this time, no further edits are allowed (just keep it at 0).
A suitable setting, had this been present, could've been named
Courtesy edit time to reason.
My request is not that important, so don't waste time and sleep over it.
EDIT: But oh wait, I just edited this post twice, and see no "Last edited" notification.
And I swear I haven't rebooted my lappie since yesterday..
EDIT2: Oh, it seems my last edit did get recorded. So, it seems the Courtesy time of 90 secs might indeed be the one controlling when edits gets recorded; that is, the total time I spend editing twice likely exceeded 90 seconds from my first post.
You could try change
Courtesy to, say,
300 seconds. Might do the job..