Possible to add log_in as rule?

I’ve been months seeking, as time permits, simply something to send our Affiliates / Users a simple reminder when they haven’t logged in for “X” amount of days.
I was so hopeful this would work but have not found a way to add that into the code (and I am not much of a coder – or at all really, to start with).

But I do know how to edit the plug in (read copy / paste / and frankenstein the crap out of it), just not which file(s) to insert it into.

The page I need help with: [log in to see the link]