How frequently do you need to re-export/import a shared cache?

Hello, I work for a small program that is looking to use bridge to better search for and organize our photos (~50,000 or so). I've gotten it up and running on my machine and keyworded some batches of photos and the search feature seems to work at a reasonable speed for the folders that have already been indexed. 

I did a test run of exporting the cache for a specific sub-folder with about 400 photos and my coworker was able to import the cache and search within that at a reasonable speed. However, the export process took several minutes as did the import process on her computer, and that was just a sub-folder in a much larger photos folder we would like to export the cache for.

My question is- how often do you need to re-export a shared cache (and have all users import that version to their machine)? Does this need to be done every time a single photo is deleted, moved, renamed, rekeyworded? I understand that the process of generating the cache for all users is time-consuming (I'm expecting several hours) but if this can be done just once a year and then updated annually I think that would be feasible. 

Thanks for the help, I only recently comprehended how the caches work and am trying to see if bridge is feasible for our organization's needs.