The original intent of my question is to see if there's support for "similar questions" feature as a user is trying to start a thread, that is, as they are typing in the title of a new thread. It will help a lot in reducing duplicate threads.
It should cache for an hour, I think (based on a quick look at nodebb package manager code). So yes - you have to wait a bit before the nbbpm refreshes. You can just install the updated version manually by using npm install <package name> from the command line in NodeBB folder.