Industry has been using these masks for years. The masks and filters come with documentation from the manufacture on filter replacement intervals depending on the use case and exact filter medium.
I do largely agree with this, but this is slightly outside of the typical use case for these masks. I'm not an industrial hygienist or other true PPE specialist, but I am a chemical engineer who has decent experience with a wide variety of PPE and it's been difficult for me to determine when I should replace my 6006 cartridges or 5P716 filter pads for home use (cleaning cat litter, preventing coronavirus).
This other brochure essentially implies the OV cartridges last up to 6 months, but those don't filter particulates. It does say however, that N95 masks become more effective as they get "dirtier", at the expense of being able to breathe easily. In this case, a tight seal would be extremely paramount, because eventually it would clog enough that you'd be breathing "around" the mask instead of through it. http://multimedia.3m.com/mws/media/447121O/filter-change-out...
They do have a web tool for calculating service life but it assumes you have at least one chemical contaminant, so the tool simply fails to calculate anything at all for hospital or home use.
The filters meant for chemical contaminants usually have some kind of active absorber ingredient that get used up which is why the replacement intervals are more defined. With particulate (which includes viruses) the only thing you have to worry about is the filter getting clogged or the filter breaking down due to old age but that isn't going to happen with indoor use unless you are talking years. That's why the filter replacement guidelines seems less specific.
