Assuming it does heat and a/c I would say three months is the max.
I date mine with the install date so I can read it thru the grille and replace every 45-60 days with a mid range filter in the summer/winter seasons where it runs more. Fall and spring may go a little longer between changes since it doesnt run as much..
When ever it is dirty, there isn't a specific time that works for every installation.
If you're in a house that has smoke and multiple pets, multiple kids, etc, you'll go through them way faster. I've had them last for practically no time at all (but that was because I was sawing through tiles inside (to accomodate a threshold piece) and the saw had no dust controlling features, so my home was thick cement/tile dust. That covered the entire place and plugged the filter up nicely.