This is a very difficult question to answer. It will depend on the concentration of the hazard and the tempo of work being applied to the task. Other factors including damage, damp and excessive dirt and contamination to the filter can have a detrimental effect to its functionality. Please remember that once a gas vapour filter is taken from its packaging it will start to absorb contamination from the environment in which it is used/stored.
It is important not to extend filters expected working life of 28 days once exposing the filter from its vacuum-sealed bag. It is unwise and poor practice. It would be detrimental to your health to smell or taste the hazardous environment during extended or prolonged use beyond the 28-day rule.
If breathing through the filter becomes difficult, excessive or laboured, it may be time to exchange the filter before being compromised to the hazard. It is important/good practice to store the mask & filters in a sealed bag away from the hazardous environment. Filters should be changed within 28 days of first use, regardless of how much use that they have had.