How long do the n95 masks last before they stop filtering out novel coronavirus?

Variable: Per CDC, discard N95 respirator that is obviously damaged or become hard to breath through, or if it is soiled / contaminated with blood, respiratory or nasal secretions or other bodily fluids or close contact with co-infection of disease that requires contact precautions. REF: https://www.cdc.gov/niosh/topics/hcwcontrols/recommendedguidanceextuse.html