I replaced the pollen filter (also known as the "cabin air filter") myself after 16 months.
This was because my wife is allergic to things like privet and she was complaining when we drove past thickets of privet.
I found a video on YouTube that showed me how to swing down the lower front dash glove box in a recent (2018?) Honda Jazz/Fit so I could pull out the existing filter (NB: make a note of which way the air flow arrow is pointing), took it down to our local auto bits & pieces shop (Repco in New Zealand), showed it to the guy behind the counter and he went and got the generic replacement. Took it home and installed it (with the air flow arrow pointing in the right direction), pushed lower front dash glove box back into place.
Quite a difference, diesel trucks no where as smelly, happy wife as her allergies were not being triggered.
So I think that the frequency of changing the cabin air filter depends on your local driving conditions - 2 years is a default recommendation.