Cabin air filter intervals... "depends".
My bought-used Honda had less than 10K on it, I was tracking down a smell and examined it... it was full of WET tree leaf and nut debris. It took a while to vacuum all the [censored] out and had to run out and buy another filter.
Since then it's garaged and I've replaced the filter once, and probably didn't need to. On the other hand, in times and cars past, I've found a mouse nest or even a dead mouse in cabin and engine air boxes.
So, my take on it is, examine it every 10K miles or so, but only replace it if it looks like it needs it. If you have a known rodent problem, examine it more often.